As expected, Valve has begun their annual wallet-busting Steam Summer Sale, bringing the usual deep discounts to PC games, DLC and even some software from today until June 21.

In the Steam Monster Summer Sale, which is what Valve is calling this year's sale, there are four categories of deals. The first two should be familiar to those who have experienced major Steam sales before: Daily Deals offer great discounts each day on selected games, while Flash Sales discount a new range of games every 12 hours.

The third category in this year's sale involves a mini-game Valve has especially created for the sale. By playing the Monster Summer Game and fighting enemies along with many other Steam users, milestones are reached which unlock new deals on games. These milestones reset every day, and that's when the deals unlocked from the previous day become available.

It appears as though you don't have to play the Monster Summer Game to take advantage of the deals unlocked by other people playing, although jumping into the game and having some fun will contribute to deals being unlocked for all. And along the way you'll get some trading cards that can be converted to a bit of cash or some Steam experience points and badges.

The final category of deals last throughout the entire Steam sale, although usually these discounts aren't as significant as discounts found in Daily Deals, Flash Sales or from the Monster Summer Game. If you have your eye on a particular game, wait until it's discounted in one of the aforementioned categories, unless it's the final day of the sale.