Olá Pedro!
Greetings to beautiful Portugal from the crazy USA! :p
Your question is a BIG one and not very easy to help with here in text only. You will probably be able get the best help with english phonetics from your teacher at the university. Or maybe you can find some english people in your local area to chat with so you can listen to them speaking?
The teacher-moderators here seem very good at what they do so maybe one of them can help you with this topic better than I can. But I wanted to say Olé to you because I only just learned a few weeks ago that this is a way to say
HI! in Portugal.
![Geeked [8-|]](/emoticons/emotion-15.gif)
There is an audio message board that some people from this group have used to post audio messages. If you have a microphone for your computer then maybe you can ask your phonetic questions there and get audio replies? That might be more helpful for learning english phonetics than text replies. If you do post audio messages there you might want make a post here to say that you did this so people will know to go listen to them.
The audio message board is
HERE (click link):
Good Luck! (Bona Fortuna?)
-michael