The commands "ban, ban-ip, deop, kick, op, pardon, pardon-ip, save-all, save-off, save-on, stop, whitelist add/remove/on/off/reload, debug, publish" are banned from normal player usage. If you are the owner of the server, you can modify these lines in your server.properties file as seen below:
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Command blocks can only be obtained using the give command and can only be successfully used by server operators in creative mode.The command block will perform certain commands when it receives a redstone current, these commands can be set by right-clicking on the block.
Unfortunately, using the /give command will only give you a pig spawner.
You cant find a giant mob in vannilla minecraft but you can sumon him using a command or a spawner.
You can dye wool with it, or you can create decorative blocks of it using 9 pieces.
You cannot teleport home in vanilla, no cheats Minecraft. However, in many servers there is a /sethome command which allows you to set a home and teleport to it using /home.