If you have a categorical IV with three levels, you will need TWO dummy variables to test it in your regression. e.g., if you have Conditions A, B, and C, your two dummies could be B and C, with A as the base case. Each of the dummies would be coded as either 0 or 1.

If your IV just has levels of some quantity, you might be able to treat it as continuous. For example, if the variable is something like time (e.g., 10 hours vs 20 hours vs 30 hours), you could leave them coded as 1, 2, and 3 and see if there is a linear relationship between each additional 10 hours and the DV. Hope this helps.