Sometimes a chain has a removable link, but do make a photograph showing where it runs (or three!)
But many bikes, built in a factory, do not have this link, so you need to buy two things, a chain splitter/removal clamp that split the chain for you and the replacement link of the correct size!
I would recommend buying a complete bike toolkit, in a travel box, not expensive on ebay, you get all the special tools in one price. Buying them separately will cost at least double.
A smaller kit for underway is also a good idea.
Find great deals on eBay for Bike Tool Kit. Shop with confidence.
www.ebay.co.uk
Maybe something like this:-
Find many great new & used options and get the best deals for Bike Hand Mini Tool Kit MTK at the best online prices at eBay! Free delivery for many products!
www.ebay.co.uk
You will need other tools if you are without such things, a good set of fixed spanners (never rely on adjustable ones, you can slip off, damaging you and your bike!), Allen keys, Torx keys.
Plastic and rubber mallets are also useful, doing a good job with no damage that a hammer will do....
regards
Andy