How do I give myself 3 green keycards? What else am I supposed to type?

Also a rocket lancher or anything with 2 worded names?

You can give yourself items natively in Rust using ownerid and the F1 console; this plugin is mainly to have a more permission-based setup to limit global admin capabilities. As far as usage goes, the command info is on the plugin page, and you can see items under our Docs link at the top of the site.

But I want to use the command it came with

I don't know what you mean exactly.

I don't want to have to enter my steam ID evry time I just want to use this but with 2 worded items: inventory.give “short name” “amount”

That is how it works as well. The Steam ID is only to give to a player other than yourself.