"How to fade in AE" 101 Guide
Click on the layer, and hit "T" on your keyboard. You will now be able to change the opacity. Decrease it to 0.
Move the time indicator to where you want the text to start fading in.
Click the little clock beside "Opacity".
Move the time indicator to where you want the text to be 100% visible. Change the opacity to 100%.
Here you go, a smooth fade in.
You can probably figure out how to fade out with that info.
Hope I helped