How can games be compressed to smaller size?

Many websites offer setup files for popular
games, which’re hundreds of MB but in a very small size. why can heavy
game( > several hundred MB ) be compressed to a few megabytes ? It’s
just so amazing. Is there any data problem with these files?
LEt’s join the discussion!

Because there’s no data files attached together with this setup files, they’re smaller than usual. this will help in case of slow connection.
I like this file type a lot, but be careful when you try it, read instructions on the Internet before install.
Some apps or games arent available in some regions, third party app store will be effective.
I often visit Amazon App store or to get the games i needed. They’re free of malwares.