AR markers are real-world markers which help devices place AR objects in the real world. Minecraft Earth doesn’t require you to use an AR marker, but they’ll help if you’re having tracking issues when placing down a build plate.
There’s no official Minecraft Earth AR marker, however, there are many available online for you to download and print out. Alternatively, you can use a book cover or something with a high amount of detail.
To use an AR marker, first, place it down on the floor or a flat surface. Then point your phone at the marker and place your build plate down on top of it. The extra detail on the AR marker will help Minecraft Earth to better track your build in the real world.
Here’s a link to download a good AR Marker. It’s an image file. To use it, press CTRL + P and print it out.
If you need help getting started in Minecraft Earth, check out the “Guide for Minecraft Earth” android app.