If you're referring to photos not being not as sharp as expected try turning off all image processing in the camera's menus. Try to understand all the settings, there are a number of focus settings. You can always reset to factory settings if you get lost and try again. Do post-processing with software, let the camera just take the shot. Use good third part software, not the freebie Nikon provides with the camera.
My Nikon D7000's factory settings were awful, far too much image processing, slowed down the camera noticeably and produced pics that were not real looking at all. Your camera should focus fine and you should be able to see it focus through the viewfinder but depending on which focus mode is selected, it may focus on the wrong object. Try and avoid the dumb settings like face recognition, use AP for low light and a P mode otherwise.
Understanding how aperture, shutter speed and depth of field are related teaches a lot about focus.
Also check the diopter adjustment wheel next to the viewfinder, it's overlooked and if adjusted improperly can cause perfectly focused shots to look fuzzy through the viewfinder but the shots will be in focus unless overridden manually. Regardless, the viewfinder won't ever give a super clear view of what the lens sees. On a DSLR, the rear screen is good for shot review and menus but poor for taking pics because of the camera's form factor.