Both ore and boku are the first person used by men in a casual situation(when you are talking with friends/someone who you are close to) as Ms Sa-sa mentions. In a formal situation, written language, and to someone who you have to be polite such as your boss, teacher, who you don't know, watashi has to be used. The difference between ore and boku is that boku can be polite while ore can't. In fact, some men use boku even in a formal situation instead on watashi, and it doesn't sound rude in most cases. Compare the politeness below... watashi > boku > ore I hope this will help you a little.

It　means　I　buｔ ore　おれ　俺　male　×business　○friend　＜　 boku　ぼく　僕　male　×business　○friend　＜　 watashi　わたし　私　both　○business　○friend　＜　 watakushi　both　わたくし　私　both　○business　（strange）friend ＜　polite　　　　　

Ore sounds more masculine than Boku.

They mean the same thing (I/me). Both are gender-specific to males, however, and they're informal.