A minecraft command?

Is there a command how to get a weapon that can create walls, for example? Would be really helpful!

No, it does not exist. But there are mods for it. Just have a look on the internet.

And btw. Which version do you play? Java, Bedrock, Pocket?

Version e.g. Java, Bedrock or handy

Bedrock

Bedrock

With / Fill x y z x² y² z² mienecraft: stone

Ok, it doesn't work there. Possibly. Realms but not otherwise. Mods can only be downloaded in Java

Unfortunately, the so-called World Edit Mod is not available on the Bedrock version. Therefore you can only set several blocks at the same time with a plugin on a server or with the / fill command.