APERTURE PRIORITY !!

One of the mode in camera which photographer like to use is Aperture Priority (A in Nikon or Av in canon) the reason that make photographer like to use mode aperture priority is that it can make you choose how to create your image, for example ; you are taking photo of your friend  with telephoto lens and you want your friend who's in foreground in focus and let the background out of focus easily in aperture priority by choosing as large aperture as your lens can adjust (f2.8, f4 ,f5.6) then focus to your friend and and  your camera and your telephoto lens do the rest. to have your friend in focus and background out focus. 

There are 3 tips to learn to control the aperture  value

1. the larger aperture value with the longer focal length lens make the thing you focus in focus and the background more out focus.
2. how to make both foreground and background in focus is to choose the small aperture like f/8 or f/11  this two value make the photo seem as you see with your eyes but still the background that far far away from the subject you focus still out focus but not as much as larger f-stop value
3. which is the most value to make foreground subject and background in focus, choose the largest f-stop your lens can (f/22, f/36)