You can add a stroke (an outline) around character shapes by clicking the Stroke swatch in the Character Palette, and choosing a color . If you want, you can then turn off the fill (so you just see character outlines), by selecting the Fill swatch, then clicking the No Color button in the Character Palette.
To adjust stroke widths, increase or decrease the value to the right of the three-horizontal-lines icon, in the center of the Character Palette. Then, from the unlabeled dropdown to the right of the stroke-width property, choose either to render fills on top of strokes or strokes on top of fills.
what's the difference between the "stroke over fill" option and the "all strokes over all fills" option? The former allows you to make this choice on a character-by-character basis (you could set other characters to "fill over stroke.") The latter is a global setting for the entire text layer. It will override any individual character settings.