Why does my Nikon D4000 change fstops and shutter speed after I take a picture?

I'm new to photography and I have possibly the worst instructor ever. Anyways, I'm using my friends' Nikon D4000 dslr. After I get the light meter reading and take the picture the fstops and shutter speed changes from what I had it on. Like I take the picture at what I set it at, right after the picture takes the numbers change. What the heck is going on? I'm already confused and now this… Help?!

Are you on manual mode? If not, they will change depending on what the camera senses as the best aperture and shutter. In manual, they will remain what you set them as

You can also make sure you don't have your bracketing option on. You will have to check the owners manual on this bc I'm not familiar with Nikon's menus. I use Cannon, but I know, at least on my camera, there's an option to set a bracket and what happens is the camera will set itself up to take 3 shots at different light settings. After you take the first shot it will automatically set itself up to take a darker photo, then after you take that shot it will set itself up to take a lighter one. It is meant to put all three together to make an HDR image.