When you roleplay, you act out the part of a character or person. You might want to roleplay an interview as part of your job search preparation.
You can say that you roleplay when you perform the part of Macbeth on a stage, although that's more commonly described simply as acting. The verb roleplay is most common when someone is undergoing therapy or participating in some sort of training. Counselors at a camp might roleplay different problems they may encounter over the summer, for example, taking turns playing the parts of campers and counselors before the campers arrive.