By shooting only in manual, you will make your life easier from here on out...so lets get to it.
Apeture is a setting controlled on your camera, that allows you to blur the background or put more in focus. The blur is often referred to as Bokeh.
Aperture is measured by a number known as the “f” number.
Eg: f1.4, f8, f22 etc
The value to which you can set the “f” number is determined by the lens you have, not your camera.
Eg. Some lenses are f3.5 - f5 or perhaps just f2.8 etc
A high aperture is f1.4
A low aperture is f22
A high aperture is a low “f” number and a low aperture is a high “f”number...confusing right, but you will get it soon.
So what does Apeture do inside your lens?
So...the bigger the aperture hole (ie the smaller the f number/high aperture eg: f1.4) the more light the lens will let through.
Also the bigger the aperture hole, the shallower the depth of field.
The smaller the aperture hole (ie the higher the f number/low aperture eg: f12) the less light the lens will let through.
Also the smaller the aperture hole, the deeper the depth of field.
Therefore to blur the background set your camera to the lowest f number for your lens (a high aperture)
Or to put more in focus, set your camera to a higher f number (a low aperture).
Any questions drop them in the comments below.