Mohammed there are 2 buttons a photographer often uses.They are the shutter speed and aperrture.Shutter speed dicides the arrenst of movement in the frame.If you try to photograph a waterfall with a shutter speed of,say,1/30 sec,the waterfall will appear as flowing mist.With a speedier shutter speed of,say,1/250 sec you would get what you really see fo the waterfall.
Aperture decides the "depth of field".In this pic I have used a wider aperture of 6.1,by which you get a pic with only the point of focus in sharpness(Here the mom).If I had used a aperture of,say f22,I would have got both the tahrs in sharpness.

There are so many articles on the internet which you can read to get a better understanding.

Regards