Nitter is like a window to Twitter, letting you see tweets without all the extra stuff like ads or trackers. It's similar to how BetterDiscord makes using Discord more enjoyable. However, unlike with BetterDiscord, you can't sign in to Nitter. This is because Nitter prioritizes privacy and simplicity. When you sign in, you share personal data, but Nitter avoids this to keep your information safe. So, you can view tweets through Nitter, but for things like tweeting, liking, or retweeting, you would have to go to Twitter directly.
I use it because Twitter has a vast amount of information but I want nothing to do with the company itself. And there are handy apps like UntrackMe for Android and LibRedirect for desktop browsers that will automatically redirect to the open source alternatives.