knocking sound from engine

[240sxHitman]

Yesterday after work around 12 or so i left and it was cold and i let it warm up for a few and drove off pressing the gas down but not to much. all of a sudden i hear a like i clicking of knocking sound coming from inside the engine and also im beginning to leak oil a little. my friend said that i spun a bearing. It happens when i drive and rev it slightly. can anyone tell me what it is and if it is the bearing how going about to fix it. I personally wont but if i know what is to be done i will kind of get a feel of how much it will cost.