Where can you download free pc games

The safest and largest gaming community that often hosts give-aways and discounts is called Steam.
www.Steam.com.

Please do not download games from sites which are torrent or pirate sites. These are violating the law, and by downloading from them, you are violating the law too.
Steam on the other hand is legal, licensed, has approval from game developers and is used by millions of gamers.