Don't worry about 3 and 4 for the time being (esp not 4).
It sounds like you might want to have a look at page 38 in your manual and brush up on "af area modes". the D3200 (if I remember correctly) has "auto" setup as it's default and this means that the camera tries to decide what you are trying to focus on for you.
If find that "single point AF" is the mode that works best for me. This means that whatever the focus point is on top of (it looks like a small square in the viewfinder) will be in focus when I push the shutter button.
Here is a link to the online manual - Page 38 gives the details of the different types of "af area mode"
As PjonesCET says, aperture priority is a very popular setting to use, but if you are quite new, then I'd suggest thay you may have more luck (initally) with the "scene modes" - just pick the one that most closely matches the subject that you are taking pictures of and go from there