When should I use the air horn during a match?

Hi everyone. Assuming I'm pretty ignorant, I'm writing here to ask for some pretty basic advice. Today is the first time my boyfriend and some of my friends are playing soccer, nothing serious, just a casual game. So I wanted to spice things up a bit by bringing an air horn or a small banner. The question is: what are the right times use the air horn (except for goals obviously)? I don't want to end up being inappropriate, I just want to support them with a bit of humor!