This link I gave you to answer the other question should help with this too:
http://soundsofspeech.uiowa.edu/english/english.htmlNo, N/T/D all have the same position for the tongue. The difference is voicing (vibration of the vocal folds) for D and N (but not T), and that air continues through the nose for N (a nasal sound!).
Sometimes T is pronounced differently. At the end of a word, it may be
unreleased meaning there's no sound after T, just the end of the word. So you might not hear T very clearly. One example is "can" and "can't", which actually can be pronounced exactly the same way (yes, that's confusing, even for native speakers of English). Additionally, between two vowels, some English dialects have different pronunciations. One in British English is a glottal stop (just a pause, in the throat, between the vowels) like "bottle" or "water" being pronounced like "bah-ul" or "wah-er", with no T at all. For American English, the same words would be pronounced with a "flap" or "tap", which is like a very short T or D. It actually sounds more like D probably, but it's shorter than both sounds. Something like "boddle" or "wadder", but pronounced very quickly (that's why it's called a flap/tap).
