This year's Spring Cleaning (https://store.steampowered.com/springcleaning) asks a few things from you on a daily basis. Today's tasks are:
- Play a free-to-play game
- Play a suggested game from the event's page
- Play a game you won but haven't even tried yet
Doing these tasks will give you event experience, which will level up your event badge. Tasks will change everyday. But you also have a list of project activies, which don't change. You have all four days to complete them. They are also individual achievements.
The event not only says you'll get a badge, but also a few inventory items whenever you reach a new level, so it doesn't hurt to try doing these even if you're not interested in the badge or leveling up your Steam profile.