Sonarr (and the other 'arrs) is just a management tool. From the servarr wiki:
Sonarr is a PVR for Usenet and BitTorrent users. It can monitor multiple RSS feeds for new episodes of your favorite shows and will grab, sort and rename them. It can also be configured to automatically upgrade the quality of files already downloaded when a better quality format becomes available.
At a high level, you tell it where your current tv show episodes are saved, and add new shows as you want. It then automates the process of searching and downloading. But you still need to have an indexer and download client. If you’re not able to find shows searching your current tracker/indexer, Sonarr won’t have any better luck.
Finding a good source of the media you want is the most important part. If you’re not comfortable with installing and managing your own server applications, the *arr stack could be overwhelming at first. The wiki I linked has a lot of good information to get you started.