Depth of field often referred to as DOF is the distance between the nearest and farthest objects in a scene or image that appear sharp. So think about it as if the camera were actually your eyes, you can't focus on everything at once, you can switch between focusing on the object closest and an object further away. You can do the same with a camera but at varying degrees.
DOF is changed by the f-stop,You will often hear this referred to as aperture, this also changes the lightness and darkness of am image so if you aren't using the on camera flash then you will have to make other adjustments.
A lower f-stop like 4.8 will produce a more intense depth of field. If you notice in the image to the left the silver nail polish is in focus and it gradually makes each nail polish go more and more out of focus.
This image is taken with a f-stop of 32.0 which was all my lens would allow me. Each lens has a different range of f-stops.
I prefer shooting with a lower f-stop so that I have a picture with more depth to it, but there are times I prefer to go to a higher f-stop. When you do any kind of landscape photography you will probably want to opt for a higher f-stop.
Like I said before i prefer to use a lower f-stop to create a focal point like the image above. You can choose which you like better but most cameras on auto will use a lower f-stop so if you aren't 100% sure about going full manual most DSLRs have an option that is "A" which stands for aperture preferred. This setting lets you put the f-stop where you want it and the camera will adjust all the rest of the settings to make you picture look more normal instead of blowing out the image or making it darker.
I hope this has helped some of you in case you were wondering what the heck I was talking about when I was saying f-stop.
If you have anything you were always wondering how to do you can always request it and I will try my hardest to make it!