Like a normal ASI, but now you can choose 3 abilities. This skill is designed to be added to legacy backgrounds, so they fit the new 2024 rules. Per the 2024 Handbook, legacy backgrounds are allowed, but they need to be updated to include ability score improvements and an origin feat. Adding this feat to a legacy background via Homebrew will give it the require ability score changes it needs to be 2024 compliant.
Note, I am not the best at homebrewing. This feat does allow you to give yourself a +3 to a single ability. If you want to stay rules as written, do not do that, instead, give yourself at most +2 to a single ability.
This feat is more powerful than a normal ASI, and as such is only intended to be used for modifying backgrounds. At your DMs approval, you can use it for other purposes, but that would not be rules as written.