Using either the Shape tools or the Pen tool, create a path keeping in mind that the type that you will add will flow in the direction that anchor points were added to the path. Then, select the Type tool and click on the path where you want the text to begin (when the cursor is properly positioned above the path, the type insertion point icon will display a horizontal line – the baseline indicator, through it) and start typing.
When working with an open path (an arc for example), Command (Mac) / Control (Win) -drag the small “x” icon at the beginning of the type change where on the path the type begins.
When working with a closed path (a circle for example), use the same shortcut as above, and you’ll notice that there is an additional “o” icon on the path which can be dragged with the same shortcut and will act as an end point, restricting the type to flow beyond it.
When moving the starting point for type on a path, you will probably notice that you can flip the orientation of type on a path by Command (Mac) / Control (Win) -dragging either I-beam at the beginning of the type, or the flashing insertion point within the type, from above the path to below the path. Note that the text will flow the text the other direction. If you simple want to move the type above or below the text (without flipping it), use the baseline shift in the Character panel.