For adventure maps, teleporters, or custom mini-games, Command Blocks are essential. However, because they can be used to run game-breaking commands, they are turned off by default.

Enabling Them in Mission Control

Stop your server (Always stop before editing core settings!).
Go to the Settings tab.
In the Game Settings sub-tab (usually the default), find the Enable Command Blocks toggle.
Switch it to Enabled.
Click Save Configuration and Start your server.

How to Get a Command Block

Once enabled, you won't find command blocks in the creative menu. You have to give one to yourself using a command in the Console tab or in-game:

/give [YourUsername] minecraft:command_block

Quick Safety Tips

Op Only: Even if enabled, only players with Operator (Op) status can edit what a command block does.
Repeaters & Lag: Be careful with "Repeat" command blocks. A single repeating command block that spawns thousands of entities can crash your server in seconds!

If your command blocks still aren't working, double-check that you have Operator status in the Players tab!