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'.