A Spotify Pre-Save allows a fan to save your album to their Spotify Library before it's street date. This allows the album to show up automatically in their Spotify Library on the day the album comes out which has the potential to increase the chances that the fan will listen and stream your album.
In order for your album to be available for Pre-Save in Spotify, you must utilize your album's magnet link. You can learn more about Magnet links here.