Are you visually challenged like me? Have you ever looked through the viewfinder and thought your camera is broken and just not focusing?
It could be the case, but it's most likely that you need to adjust the diopter.
You can usually find a little dial on most DSLRs to the right of the eyepiece (viewfinder), that you can adjust.
The basic function of an adjustable diopter is to fine-tune how you see what the camera sees.
This can be simply done by following the following steps:
1- Turn your camera on
2- take off the lens cap and point it at a well lite area
3- turn the diopter all the way to the positives
4- slowly turn the wheel to the negative whilst looking through the viewfinder until the focus points appear to be at their sharpest
P.S be careful not to get dust on your sensor when doing this exercise, I recommend doing in inside.