Put simply, esports is competitive level gaming. It's teams of people playing games against each other at a professional level, regularly winning huge sums of money as prizes.
These eSports players are contracted to play for a variety of different organizations, much like a football or basketball player would be.
These teams practice and compete on their respective game just as a footballer or other sportsperson would too. Depending on the game they play – from shooters such as Counter-Strike: Global Offensive esports and Call of Duty esports to the multitude of other genres like sports titles and battle royale games – there will be a number of tournaments and events each year with hundreds of thousands of dollars in prizes up for grabs, sometimes even entering the millions.
Most games will have ranked modes and playlists you can jump into via the game itself. You'll be matchmade with others online and often – but not always – this mode will have slightly different rules than the standard game, with some restrictions or timer differences. Largely though, it'll be the game you're familiar with.
If you've reached the stage where you're frequently winning in ranked play, there's a good chance you're ready to make the step up. This is where each game varies, because games that have first-party esports support from the developer themselves will have an easy method to compete, like Fortnite's in-game tournament system.
Other titles such as Call of Duty and Rocket League will rely on third-party platforms like Gamebattles, ESL, or FACEIT to provide esports services. All three work in similar ways, by providing leagues and tournaments for players to compete in. There are some nuances in how each one operates, but the gist of it is you can link your online ID, whether it's PSN, Xbox Live, or one of the many PC services. From there, you can register for leagues and search for a competitive match. Don't worry about feeling like it's a big commitment; free-to-enter leagues will usually work on a "play when you want" basis, rather than having scheduled match-ups. There's often cash rewards on offer and if your end goal is to compete at LAN events in person, you need to prove yourself in these online matches first.
From there, once you've either proven yourself as a solo player or got a team together, you'll be able to play in open qualifiers – which will have scheduled match times and are more organized – to see if you can make it as a full-blown pro. Usually, these will also be online, but again, every game is different and sometimes there'll be local events like Call of Duty's City Circuit which allows anyone to represent the various franchised teams. It can't be stressed enough however that the specifics for each game will be different, so make sure you do your research. If you're skilled enough and perform when it matters, there's a chance you'll be signed to an organization, at which point the sky's the limit!
Reference credit: https://www.gamesradar.com/what-is-esports "What-is-eSports? A beginner's guide to competitive gaming, James, Ford, February 13, 2020"