A command unit based on its functionality to do in Minecraft, like all the other blocks, unfortunately, impossible. However, there are other ways to obtain it.
If you are the Creator of the server, then you can use a command block. You can also get it if I get admin rights.
But even when you have your own Minecraft server, or not have a friend who can make you an admin, you can create a team using cheat codes. However, you have to play on the server that supports their use. To do this, use the command /give @p command_block,
To the command unit had the opportunity to work mltiplayer, open with Notepad the file and write enable-command-block to true.
If you have to make a command block in Minecraft with the admin rights or with cheats, creative mode, open the interface, right-click. Here you can enter the desired commands. Your request will be carried out when you activate the Redstone, the corresponding command block.
The command block using written commands, you can control the map, kill the entities of the selected type to write messages in chat, as one, and immediately all players.
If you make the Minecraft command block, you should know the commands to use it. Full list of queries you can see it on the website