There are a lot of parties all the time. It is very easy to find something any thursday, friday, or saturday.
The frat parties are the biggest and most extravagant. However, there are also always other parties which may be less exclusive. There is always something going on and we also have access to all of Los Angeles nightlife. Downtown Los Angeles, Koreatown, and the Arts District are all very close to USC. Hollywood areas are slightly farther, but you will find you have a lot of options. With Uber or the Metro, nightlife is accessible.
USC has amazing parties and events almost every night. Most are difficult to get into if you are a boy, unless you are a part of a fraternity. Women are let into every party.
There are a few bars on/near campus that are pretty chill for laid back drinking, watching games, etc. There are many bars downtown just a few minutes away by bus or uber. There are lots of clubs downtown and in Hollywood, including many that are 19+, so underage people have a place to safely party.
If you like to party, rushing a fraternity or sorority is a must because that's easy access to the row.
USC fraternities and sororities are pretty famous for throwing ragers, and the row lives up to the hype.