Quick Descripion: Draw the arc you want as a baseline. Using the Text-on-a-Rope tool (looks like text cursor on a line) click on your selected path and begin typing. Highlight text with cursor to change size, font, and other attributes.
Drag the starting cursor of the text line to fine-tune positioning, or drag to INSIDE of curve if you want it to run the toher way. Command-shift-C (on Macs) or control-Shift-C (PCs) will center your text on the path. Adjust kerning after positioning for best results, especially with line that is not strictly circular (like an ellipse).
You could then convert to outline for other enhancements/embellishments (such as blends, etc.)
Hope this helps.