There are still hundreds of players who weren’t selected and now those players will be hoping that one of the 32 teams in the league contacts them for a shot to continue their careers. All teams can have up to 90 players on their roster when training camp begins, so many teams will sign as many as 20 undrafted rookies.
It seems that, at least with the Los Angeles Chargers, that one of those players always ends up competing for a roster spot or even winning a spot on the roster. Recent examples of this include Austin Ekeler, Trevor Williams, Adrian Phillips and Michael Davis.