If you wear glasses, and you're not getting sharp focus in the viewfinder, you might need to adjust the diopter to get the clearest photos.
First, do try using Live View, to see if the camera focuses properly in Live View. It uses a different focusing system in Live View. If this works, your lens is fine.
Then, put the camera in the GREEN auto mode, and put the lens in AF mode. Make sure you have plenty of light, and your subject is an easy subject to focus on - something a normal person would photograph, not a piece of paper, or a plain white wall.
Looking at the viewfinder, you'll see a little "gear" or wheel just to the right of the viewfinder. That's the dioptric adjustment. Remember where this is, you'll need it in a minute!
Put the camera up to your eye, and push the shutter button halfway down until you hear the focus confirmation beep and you see at least one AF point light up. Is your red focus point blurry to you? Is your scene blurry? If so, adjust that little wheel to the right of the eyepiece until it becomes clear, and try again. If your prescription is too strong for the dioptric adjustment, you may find that you need to get a different eyepiece that accounts for your vision. We make those, too!
You can learn about the Diopter on page 36 of the manual, HERE.
