The main purpose of its usage is it helps the torrent clients like BitTorrent, Utorrent, qTorrent, etc to communicate with each other such that it can find more peers and seeds enabling the user to download the relevant torrent file(let it be movies, songs, videos, images, documents or anything) quickly.
In simple words records the statistics of the torrent file across the distributed network. Torrent trackers is a software tool that tracks the information of peers and seeds for a torrent file. torrent is an extension used for BitTorrent file format.