Combined with your previous post, I'll guess that you're a brand-new AE user, or very close to being one. You should know that AE is a beast unto itself, unlike almost any other multimedia application. Experienced Maya and Cinema 4D practitioners have problems with AE if they don't learn the basics.
In other words, you need to learn to walk in AE before you run. You can't jump into the deep end of the pool; if you do, you'll have a big lead weight around your neck.
Over the years as the application has evolved to accommodate more and more capabilities, AE has accordingly picked up a growing list of little details you need to know. Even if you know Maya, FCP, Motion, C4D, Vegas, Avid... what have you, a solid grounding in the basics is essential. And here's a good starting point: http://blogs.adobe.com/toddkopriva/2010/01/getting-started-with-after-eff.h...
This has been complied by the guy at Adobe who used to write the manual for the application. He's still a big Adobe muckety-muck. He won't steer you wrong -- it's in his best interests not to do that.
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