I've never used a tool just usually a pair or needle nose plyers or something to snap it on. It's not easy to do but once you do it a couple times it gets easy. when tightening it usually I like to have about 1" total up and down movement in the chain. There is a spec to this in a manual I am sure but that is what I go by I like my chain a little tight.
A chain breaker is for breaking of links in a chain. When you buy a new chain it comes with extra links you use the chainbreaker to remove what you don't need. I usually us a cutting wheel to shorten my chain.
Good luck
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