As per Quinn's request, here's how to simply make text type on screen, like a typewriter.
1) Create a new text layer and type your text.
2) With the layer selected and it's parameters open, open the pulldown "Animate" menu and select "Opacity".
3) This creates a new "Animator 1" property for your text layer.
4) Open up the "Range Selector" property, and then open the "Advanced" property.
5) Now turn the "smoothness" to "0% and turn the "Opacity" to "0%". Then, all that's left is to animate the "Start" property. Set a keyframe for "0%" at the beginning, and set it to "100%" on the frame that you want your text to be fully on screen. That's it!