Can someone inform me on the IRA?

i wana know where they came from, and any kind of information ..im part irish and i have irish friends straight from ireland and theyre alyways talking about how they hate the british which is kind of dissing towards me since i have some british in me but like why do they have sucha a hate towards the british? i know they have to do with the ira but i dont know exactly and why do the irish love and at the exact same time like the ira? when they even kill there own ppl?