There are a few different ways to outline text in After Effects. One way is to use the built in 'Stroke' feature. To do this, simply select your text layer and click on the 'Stroke' button in the 'Effects' menu. This will open up the 'Stroke Options' window, where you can select a color and thickness for your stroke.
Another way to outline text is to use a tool like the 'Bevel and Emboss' tool. To do this, simply select your text layer and click on the 'Bevel and Emboss' button in the 'Effects' menu. This will open up the 'Bevel and Emboss Options' window, where you can select a color and depth for your outline.
For more detailed instructions on how to outline text in After Effects, check out this helpful video tutorial from Motion Graphics Guide.