“Prop Blocking”, is when a player blocks another player, entity, room (and so on) with one or more props!.
“Fading Door”, is a tool used to make doors out of props that can become nocollided and invisible when activated.
“KeyPads”, are a tool that let you set a preset password to let other users to use your keys. i.e. By entering the right password might use the owners “1” key on the number pad that control’s his/her hover ball.
You will need to head over to the servers web site (if they have one) and read there rules.
The Gmod community is good to new players so don’t stop to ask for help.