AT ON IN

I am confused, because I searched on internet (or in?) the right use of at/in/on.... and I couldn´t understand the reason for the use each <em>or </em>how each was used.
Can you help me?
I use "at" for common places (school, university, airport...) but "the park" and "football pitch" I think these places also are common places. What is the difference?

soy nativo, no profesor

preposiciones son dificiles en inglés y español; tardan mucho tiempo aprender

at the park, at college, at the university, at school, at the airport, at the football stadium

AT ON IN

I am confused, because I searched on the internet (or in?) for the right use of at/in/on.... and I couldn´t understand the reason for use each how each one is used.
Can you help me?
I use "at" for common places (school, university, airport...) but I think "the park" and "football pitch" I think these places also are common places. What is the difference?