The outline effect is applied from the Layers window.
- Select the text layer you want to add an outline to.
- Open the effects menu in the bottom of the Layers tab - it looks like fx.
- Choose Outer Glow.
- Adjust the color, spread, and opacity of the outline using the sliders in the popup.
Experiment with this menu until you create the desired outline.
If you rasterize the outline effect, it will become an inseparable part of the layer. This is useful if you want to apply the same effect again.
If you decide to permanently apply the effect, you can rasterize the layer by right-clicking it and choose Rasterize Layer Style.