Not that difficult at all. I suggest you take a look at the wiki entry:
https://wiki.alliedmods.net/SQL_(SourceMod_Scripting)
I believe if you use SQLite you have to create database tables via the plugin. Not too sure though as I've never really used it.
SQLite doesn't require any hosting program as it's a local file stored inside of the sourcemod folder. MySQL on the other hand does. Usually this is externally hosted and can be used for multiple servers.
You don't really need to worry about SQL Commands specifically, just syntax and the language really. This is one place you could learn about the language:
https://www.w3schools.com/SQL/deFault.asp
You could also look how other plugins handle their databasing as well, in fact I recommend doing this as it'll help you understand the flow of SQL in sourcemod