A good basic exercise is this:
Find a well lit subject. Put your camera in [P] mode. Put ISO and WB (white bance) in Auto. As you get ready to shoot, press your shutter release down halfway and hold. Now look at the screen. It will show you the recommended shutter speed and f/stop. Take the shot.
Now put the camera in manual [M] mode and set the f/stop and speed to the exact same settings you saw in [P] mode. Now decrease the f/stop one time. What you just did was cause the shutter open more, letting more light in. Since you are making the shutter open bigger, you will need to decrease the shutter speed to make up for the greater opening. After adjusting these two settings, take the shot.

Now compare the two images. The second one should have a blurrier back ground and the subject should be alittle sharper.

This is the basics of how f/stops and shutter speeds work with each other.