ok so other day, i wanted to replace spokes on rear wheel...i took off wheel and removed ball bearings, only to discover that theres this weird shaped thing holding the gears on to the wheel...i had no tool to fit it...can you guys tell me the name of this tool? and are there many sizes for this tool? or is it universal?

It's called a cassette lockring tool.

Read: https://www.parktool.com/repair/readhowto.asp?id=48

First, why are you removing the balls to replace the spoke?
Second, it sounds like you have a cassette and need to remove the lockring. If so, then you need the cassette lockring tool. Most LBSs should have one to buy. Most likely it is the Shimano one, Park Tool FR-5. You will also need a chainwhip.

thanks for very quick reply