How does horoscopes and astrology work?

Is it some kind of universal, star and galaxy, position of the planets thing? Or is it just coincedence, all in your head? Or, is it possible that it’s just what time of year you’re born in, in relation to the weather and certain events that happen that time of year and it’s effect on your upraising and life experiences?
Do you believe in any of it? Why?
I’m a leo and apparently I love attention and myself. I also am creative, bossy and dominant, among plenty other traits.
For the most part, I find this true. Even other leo’s that I have met seem to fit this description. And my opinion is that its because we are born in the summer, a very active time of year, no school, time to enjoy being with friends and being yourself and doing what YOU want to do and not what your teachers tell you to do.