In this directory, you will find

leagues.json - A JSON file enumerating all leagues in the dump
###_seasons.json - [###: League ID] Enumerating all seasons in the dump
###_####_matches.[json|csv] - [League ID, Season ID] - The match data for each season in both JSON and CSV formats
###_####_players.csv - [League ID, Season ID] - The player data for each season in CSV format

In the *_matches.json files is also a UserMatches section which maps PlayerIDs to one another that represents the Player Linking functionality.