You will initially have to shorten the chain before you fit it, for this you need a chain rivet extractor. Websites like Sheldon Brown will tell you all you need to know about this, it is fairly straightforward. Many multi-tools come with a built in chain tool that will do for roadside emergencies. It is actually rare for a chain to break unless it has been bodged during fitting, though one of mine let go recently while climbing a hill. The first one I have had break in over forty years.