What is it like to know two languages?

To all multilingual ones here, I pose this question: what is it like knowing multiple languages? Do you think in different languages, change when the environment does, or switch between them randomly? Do you ever get your words mixed up (i.e., you're talking to an English speaker but instead of saying cheese you say queso)? Do you find that knowing another language helps or hinders your understanding of your native one?

Pick and choose whatever you want to answer, but thank you for your time either way!

I am fluent in two languages, however one of those is a minority language which is a little limited. Doesn't have words for as many things as English does, for example. Nationalists invent neologisms to try and keep up, but as a fluent speaker I find them silly.

Anyway, I speak it all the time with my mother and no one much else. I try and listen to the radio station in it sometimes to see if I can still keep up like I could when I went to school and was mostly educated through it.

It's also pretty cool to be able to speak to my sister and whatnot with other people not understanding. Being part of something with less than 1m speakers world wide feels good, too.