You allready have 2 stores on samsung devices: goole play store and the samsung store. They both work the same. Choose an app and install it. They work like any other app...

You can also download apps from the "f droid" depository.

You can even turn on developer options and install raw apk files. Those can contain viruses. (Or more probably: are pirated)

Funny to have this discussion hacker news? I thought everyone was using side loaded apks from apkmirror when you needed an old version.