Dota 2 is entirely free to play for anyone with a PC, Mac or Linux system capable of running it. All you need to do to play Dota 2 is create a Steam account and download the game, then you can play the same game the professionals play for free.
When it comes to being in the game and playing against others, someone who has not spent a penny on Dota 2 will have the exact heroes to choose from as someone who has spent thousands and will have no competitive disadvantages.
All of the 119 heroes are available to every player for free, unlike other MOBAs such as League of Legends.
Valve makes money from Dota 2 in a variety of ways. One is the selling of cosmetic items for the many available heroes and other areas of the game.
These items that can be purchased for real money, offer no competitive advantages, they just change the look of certain things in the game and give players a chance to show off.
Dota Plus is a subscription service that costs $3.99 per month and offers several bonuses for players. These include extra stats about your performance, further progression challenges and exclusive cosmetics along with some other bonuses.
Dota Plus is not a requirement to play but is something people who play a lot of Dota will want to look into.
Valve also makes money from the annual Battle Pass that is released to increase the prize pool for The International. The Battle Pass offers some cosmetic items, challenges to complete and other bonuses, with 25% of all purchases of the Battle Pass or extras for it going into the prize pool of The International.
The other 75% goes to Valve, who use some of that money to put on The International tournament.