Wire ligatures, like elastic ones, can be single – going around one bracket – or woven around several or all of the brackets in an arch. A single wire ligature does the same job as a single elastic: it holds the archwire in the centre of the bracket. A long wire is usually tightened around several teeth to stop them from moving apart. It can be used, for example, to hold the result after we've closed gaps with an elastic chain.
This answer is for general information. Your own case needs an examination by an orthodontist.