When learning photography, remember to treat each problem separately.  I.e. take away variables, just like in high school math. Don’t say “yes I see that aperture does this or that, but why is the colour wrong?” – different problem.

So aperture gives you narrow depth of field. Lower F-numbers give you blurrier backgrounds. Tue. But so does getting closer. The following images -of a kind student volunteer- were all taken with the same lens focal length and the same aperture and shutter. All I changed is to get closer.

See how the background gets blurrier?

(The reason: in percentage terms it is getting farther away, i.e. related to the foreground, as a ratio).

So the lesson? When learning, change only one thing at a time and see what that does. (That is why a prime lens is better than a zoom lens).