should I say I will fetch it for you or I will go & fetch it for you. meaning get it for you. right?
Yes, it means 'get it for you'. Both versions are correct. It's the same as: I will go and get it for you. I will get it for you. Some grammarians would prefer to see: I will go to get it for you, but there is a strong case for 'go and get' being correct. (It's two actions.) I will run and jump. I will run to jump. Can you see the difference? I suspect your question is centered around this grammatical point as opposed to the meaning of 'fetch'.