My suggestion. Learn to play with aperture first. Setup something static in a row, like drinking glasses. Then set your camera so that you can change the aperture. Now, set your aperture to the largest (smallest number, ie f4). shooting from the end of the line of glasses, so one is close and the one at the other end is furthest away. focus on the middle glass and take a shot. Then change to f10, and do the same, then f16 and do the same, then f22 and do the same. Now go to your computer and compare the shots. Look at what is and is not in focus. This should give you an understanding of how changing the aperture affects what is in focus (front to back).

From this come back to this thread and tell us what aperture you would use to get a portrait of a person in focus, but the background blurry.