<img src="/ubbthreads/images/graemlins/smile.gif" alt="" /> no need to feel stupid... these are questions we hear all the time... you not the only one.
The game takes a little while to get used to the act changes, since you cant go back.
Make sure you take all the loot with you that you want when you go to act 2, otherwise they will be lost to you.
Other things that happen on act changes:
Unique items become normal items (but they keep the stats they had)
You can now SELL the unique items that has been changed.
In Act 4 You will lose a set of teleporter pyramids (that you will find shortly in Act2)
All hostile creatures (the normally neutral ones) will be come neutral again (if you made them hostile by killing one)
Your battlefield instructors (merchants) will teach higher levels of the skills they teach.
And a couple of more small things.