A quick google search is able to explain far better than we can here.
Since you are in Education Edition, Place some Deny Blocks near the bottom of the world. Only players with World Builder status will be able to modify this area.
Here is the entry from the Gamepedia Minecraft Wiki:
When placed, allow blocks let users without world builder status place or destroy blocks in the area above them, while deny blocks prohibit users from placing or destroying blocks in the area above them. Neither blocks will affect the area below them. If two allow or deny blocks are placed on top of one another, the block that is highest takes precedence. If an allow block is placed somewhere with a deny block below it, the space between the two blocks will be protected while the space above the allow block will permit users to place and destroy blocks. The converse is also true. However, these blocks are not impossible to destroy, as they can still be destroyed by mobs like ender dragons using commands.
Users with world builder status are able to place and destroy blocks regardless of where any allow or deny blocks are placed.