I'm new in video editing right? ok.
I thought Adobe Premiere Pro 7.0 was a very complete tool to edit videos or images (as well as audio), but...

I've seen in YouTube very cool effects that are made in "After Effects".

Is After Effects, a complement to Adobe Premiere Pro? or just similar products?

which one is more complete?

Also what's the "CS3" meaning?

kinda confused.

gracias.

The CS3 handle is just the latest version numbering. CS standards for "Creative Suite" which it is now part of.

Premiere Pro is a video editor.
After Effects is a compositing tool. You can sort of think of after effects as a special effect tool. It's more than that but if you think of it that way then you're on the right lines.

So, yes, they do compliment each other although there is an overlap in functionality.

So if you think of yoursefl as wanting to 'edit video' then Premiere Pro is Adobe offering for the job. If you want to composit video and do special effects including blue screening and masking then add After effects to your arsenal.

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I'm not young enough to know everything!

There are many things that can be done with Premiere Elements, you might want to check into that as well. The price is much lower and the power of the program is quite good.

Not to mention that the learning curve would be a bit less and you can always move to Premiere Pro when the need arises and you will have a head start because the two programs are very similar in many ways.