Custom Block Editor

The custom block could be obtained by commands and the are basically 3D map blocks. You first select the block and then it opens an UI panel in which you can type [X] [Y] [Z] coordinates and then [X] [Y] [Z] coordinates which map the area which you want in the custom block.

There's another way. You first go in the UI and then click on the second slide to fill in the blocks yourself. To do that, you can check the "Place in block" toggle and then grad the materials from your inventory and start building. When you build the block will shrink down to the size of a pixel and you can make wonderful arts and stuff!

You can also write functions, which are in codes like: /moveblock or /animatepos so that you can make a function. Like in Java edition it shows the next step like: /fill [you didn't write the following part:] Start Pos End Pos [Block State]. You cant place the custom block inside a custom block, but you can put command blocks and entities.

Hopefully you weren't tired out by reading =)