Build plates are one of the core elements that make up the gameplay of Minecraft Earth. It's probably easiest to think of a build plate as a personal Realm or Plot that you can build on.
You can even invite friends to work on your build plate. You also aren't limited to just one, and can buy more. You'll get resources for your build plate primarily from tappables and adventures.
In this mode, you place down your build plate the size of a tabletop. This mode is primarily used for building, and where you can also invite friends to help build with you.
Keep in mind, resources in Earth are finite, and tabletop mode isn't a 'creative' mode. You will use up resources, like blocks or items obtained from your adventures/tappables.
Life-size mode lets you scale up your builds to life-size, and place them around in the real world to actually explore your creations. You can even invite friends to take a look and play around with you.
Microsoft has also mentioned that there will be a way to permanently place down your builds, life-size around the world, however this will be heavily curated.
Playing with Friends
You can invite friends to help build on your build plate, but keep in mind that means they can also destroy blocks that are placed down there, so only invite other players you trust.
Keep in mind, your build plate has to be in tabletop mode, and you also need to be in the same location to build together. Also, if the owner of the build plate closes the game, the other players are disconnected.
To invite friends to build with you, you just simply have to hit "invite friend" which generates a QR code. Nearby friends will have to scan this code using the "join friend" feature to interact with your build plate!
You also have the option to invite friends to play on your build plate scaled to life-size, which is also known as play mode. This is just an instance of your build plate though, and nothing gets saved.
This means you and your friends can pillage the build, going ham, destroying mobs and houses without worry. After the session ends, everything goes back to normal and nothing is lost.
Upgrading & Obtaining Build Plates
Using the in-game shop, you can upgrade the size of your build plate, or even buy more. You'll also unlock a new build plate to play with every 5 levels in-game, along with more resources to build with.