In survival mode, this only works if you actually have the block you’re facing. Otherwise, nothing happens. And in creative mode, whether you have the block in your inventory or not, it will always ...

Obtaining command blocks In creative mode with cheats on, open the chat console and type a command like “/give @p command_block” or “/give [username] minecraft:command_block 64” to receive them. These ...

You can get a command block in your Minecraft world using a special chat command. You'll need to have both Cheats and Creative Mode enabled in your Minecraft world to ...