You're question sounds a little vague. What are you trying to do?
If you're trying to draw a simple arc, that's pretty easy to do using the pen tool. You can stroke the path afterward to how ever many pixels in width you need.
If you're trying to make a text element do an arc effect, go to Layer Menu > Type > Warp Text.
For anything more complicated than that (or anything that may ever need to be cut in vinyl or routed at all) this sort of thing really should be done in a vector-based drawing program like CorelDRAW or Adobe Illustrator.