It's easy right? Just select your text, go to Type > Create Outlines and then apply your gradient. But what if you need to edit the text? You can't after you create outlines! This tutorial will teach you how to add a gradient and still be able to edit your text!
Using the Type tool, type out some text.
Using the Selection Tool, click on your text to select it. Now go to your Appearance palette. If you don't see it go to Window > Appearance. Click the little arrow in the top right of the palette and choose the following:
In the Appearance palette you'll see a new layer for a Fill as shown below:
Now you can apply your gradient! Click on a gradient swatch or create your own. If you don't see your Gradient palette go to Window > Gradient. I used a white to green gradient on my text.
The best thing about it is that you can still edit the text!
The Appearance palette also has the option to add additional strokes. That's how you can create text with multiple strokes. Here's what I came up with after adding two strokes: