There are lots of adobe tools to learn but if you want to go in multimedia field adobe after effects is best tool to learn. Adobe says, “With Adobe After Effects® CS4 software, you can create compelling motion graphics and blockbuster visual effects with flexible tools that help save you time and deliver unparalleled creative power.”
But the question is from where to start learning after effects. Yes there is a web site, adobeTV, where you can find beginner, intermediate and advance video tutorials of after effects.
Here is the list of video tutorials to get started with. You can play them directly here or you can click the link to visit adobeTV and browse more tutorials, as here i just have listed tutorial for beginners.