You need to provide a lot more info. What MP4 file? How do you preview audio? What system? What version of AE?
It's a video that I recorded with me camera right. And I import it in AE cs6. On my acer aspire6930 windows 8 64bit 40968mb of ram
3568mb used nvidia geforce 9300m gs. How should I preview my vidoe and audio?
How should I preview my vidoe and audio?
This page explains how.
After Effects is not an editing program and it's actually a fairly deep program. If you try to jump in without a good foundation in the basics, you will just end up frustrated. I would highly recommend that you start here.
Listen to Mylenium about providing more information to get a better answe.
Listen to Szalam about previewing and learning the basics.
And listen to this: 4 gigs may seem like a lot of memory, but it's basically just enough to runn the Operating System and keep After Effects open. You say you want to actually DO something with AE? Get yourself more RAM. Think about 16 gigs. 24 or 36 gigs would be even better.
AE's a RAM Hog.
Thank you very much this is great help and I total understand what you mean about trying to jump in this amazing program. I have had a bit of frustration.