Linux had package managers long before app stores were a thing. Package managers just mean that instead of downloading NotAVirus.exe from some sketchy web site and hoping it’s the app you’re looking for, you get your software from a (trusted) central source, that is community maintained so you can be sure that it’s up to date and secure.

Of course, you can still manually install things. Or even build from source, giving you nearly unlimited options to tweak things as you like. But the good thing is, you don’t have to.