I wish that undergraduates were taught more about research, and had more experience doing research. Panini is right about some misconceptions in your post, but from what you wrote my guess is that those are due to what you have-- of more precisely have not-- been taught. It's good that you're asking about this.
There are many different points we could discuss, so I'll just try to outline a few.
First, Linguistics grad students often have diverse backgrounds, not necessarily undergrad experience in Linguistics. So that's not necessarily a problem. Anything you can do now to set yourself apart is good. Maybe just looking into research on your own. Maybe looking for a summer school (often a two-week program somewhere) for Linguistics (check LinguistList for announcements: they've been posted recently for many places). Or maybe some relevant life experience such as joining the Peace Corps and teaching/learning language(s) along the way. None of those are required, and there are other things you could do too, but having something to set yourself apart in the admissions process would help. Grad program admissions are getting more and more competitive, and while there are no strict requirements, there will be some students applying who do have a strong background in Linguistics and even have published research. (And other students will have uniquely qualifying backgrounds, like international students who can teach a language that is needed on campus and who bring a relevant, different perspective to the program.) So look into programs that might interest you (and look for one that is a good fit, not just the one that is the "best" on paper-- the best fit for you personally is going to be most likely to accept you as well), and see what requirements there are, and what you can do. You can contact the programs too.
Regarding research, I've heard the generic advice of "check Jstor" too often. Now, Jstor is useful. But it's useful because it gathers so many journals together, and many universities have access to it. But it actually is not very useful for the newest research, specifically because the strongest coverage in Jstor is older materials, and even for current journals, there's often a 1-4 year delay before new issues are posted there. It's also not a very useful search engine. Google Scholar can be helpful if you use it well,* but it won't magically give you all of the most relevant information if you don't know what to look for.
As a general introduction to the field, I would recommend two things, both of which can be done (mostly) online:
1. Subscribe to (or just browse) LinguistList.org which is the general source of information and notifications for linguists. It's widely used, and just about everything you would need is posted there, such as jobs. But for you right now, the most important thing is that almost all new publications, including both books and journal issues, are posted there with tables of contents to browse through. The best way to know what's going on in the field really is to browse through what's being published right now. No need to read all of the articles, of course, but browse until you find something interesting, and then see if you can read it. Many preprints (basically drafts) are posted by the author on their website or elsewhere as open access, and some journals are open access today. Otherwise, you usually can visit a nearby university library to get online access to many online sources that way, but that would mean making a trip there (and check the access policies, especially given the pandemic, but usually at least some school near you will have public access one way or another).
2. Attend a conference! You can just sit in the audience and listen to the talks. Sometimes there's a small (or maybe large) fee, but it might be waived or reduced for students (and usually I think you'd count as a student, i.e. as a prospective student, rather than in the same category as a professional or faculty member). And some are free. There are many conferences, probably a surprising number even locally around you, and you can find something that interests you. For language acquisition there are at least a few dozen each year (internationally). These are all posted on LinguistList, so take a look and find something that interests you. But right now especially it's even more convenient, because, given the pandemic, many conferences are online so you can attend from anywhere. Don't feel out of place because you're just beginning: that's a great
reason to attend a conference, not one you should feel shy about. You learn a lot from listening, and you'll find what excites you, and what bores you. That's good. You'll know what to focus on in your own research. You might also meet some people who can give you advice (although that's harder, but not impossible, in an online context). But if you're still not sure about that, you could also revisit some previous online conferences, where the videos have been posted to Youtube, for example. There have been many, many conferences like that over the last couple years during the pandemic. I'll let you search online to see what interests you the most, although for a very general series of accessible talks, you might check out these, all available on Youtube, from the Brazilian Linguistics Association (mostly in English, but a few in Portuguese, Spanish or other languages):
https://aovivo.abralin.org/lives/*Regarding how to use Google Scholar and other databases to find references, it's tricky if you don't know where to start. Part of becoming a competent researcher is learning the relevant terminology for your specialization, and that can take years to fully work out. So just start with things that interest you, and start to do searches related to those topics and keywords. Wikipedia could be a good place to start, just to get some general ideas, then look at the references cited there to see what is relevant. A really good trick is to find an older, general reference that's been cited by many people since, and then look for that as a "reverse search" on Google Scholar using the "cited by" option: then you'll see who has been doing research in recent years related to, e.g. Lenneberg's classical ideas about the "critical period" in language learning (a popular but controversial topic regarding age effects), just as one of many, many examples. Next, you can find a current paper, and then look at its reference list, and then go back to another classical paper that way, and continue in that back-and-forth pattern until you find what interests you. It takes some work, and some practice, but it's really the only way to get deep into the best references for a topic. The other approach, hinted above, is to just look at current research (e.g. latest journal articles) and then start trying to decipher those. That's going to be difficult/advanced because they're not meant as teaching materials but as cutting-edge research, but if you follow the same process of reading some of the central references, you might be able to teach yourself that way, if you're the kind of person who likes to be an independent self-taught learner. One word of caution: don't assume that the most popular references are necessarily the best. Look for yourself. But if something has been cited by a lot of others, it's probably worth knowing what it is.
Something else you might try on your own would be online classes in Linguistics, if you want to approach it that way. There are limited options, but you'll find some open access course materials (at MIT, for example, among other places) you could browse through. I also recently found this, which I haven't tried myself, but did look interesting:
https://oer-vlc.de/