Samsung devices come with their own file manager "My Files" which lets you browse both built-in flash and SD card but not network. At least before it didn't let you delete or rename files so it's kind of limited.
For apps, Solid Explorer Classic is pretty good, it has ads on the bottom until you pay $1.99
estrong ES File Explorer once had a good rep but has gone to total poo with ad-infested popups and as much memory usage as a browser or the OS. The huge number of always-on processes cuts battery life with ES file explorer installed in half, plus estrong is based in China requires granting both storage and network access... Stay far away.