There are many ways to separate an item in a shot for compositing. They are all laid out here:
Before you jump into that, though, you need to work your way through the basics. After Effects is not an application that you can just dive into the middle of. Start here to learn After Effects: http://adobe.ly/bjBT3P
As Todd states, there are many different ways to do this. But all require a basic understanding of After Effects.
If it's a still photo...I personally would do it in Photoshop. You can then import the PSD file into AE to use it in a video.
Thanks Todd - checking this out right now.
After several hours only, I have realised there is a learning curve here.
Starting to get the hang of some concepts by trial and error - free web tutorials etc.
Josh - I see the point - don't have Photoshop so will continue playing.
Looking foreward to making some stuff to put my music to eventually.
> Starting to get the hang of some concepts by trial and error - free web tutorials etc.
Please start with the second link that I provided. There's a lot of misleading garbage out there, and the (free) resources collected on the page that I linked to were chosen for being the best for someone just getting started.
Doing it right now.
BTW the first link you gave has already got me there with this still image.
Having fun already - amongst a little frustartion of course.