Okay, so the kanji itself means buddy and so does the word, but it also means you as well. This is one of the several ways to say "you" in Japanese, and this one is kind of an "affectionate" you. Maybe you'd say it with someone you're close to. Maybe you'd say it with a girlfriend or boyfriend. You wouldn't want to use it with your boss or teacher, though. Make sure to keep that in mind. It's kind of like saying "hey buddy" or "hey you," after all.
Since this word is made up of a single kanji, it should use the kun'yomi reading. When learning the kanji, you didn't learn that reading, so here's a mnemonic to help you with this word:
Who's your buddy? It's Kimmy (きみ)! If you know a Kimmy, imagine her. If you don't, find a famous Kimmy or make up a Kimmy to imagine. You ask... is it you?? Wait, you're my buddy?
Are you perhaps Koichi's younger sister?
The curry you make is the best in Japan.
You taught me the importance of taking a shower every day, right?