The first time you use the Map Editor you will be greeted with a help screen. You can view this help screen again at any time by clicking the ?⃝ icon in the lower right of the map.
You can view a 10x10 meter grid over your map by clicking the icon in the lower left corner of the map to open the visibility layers modal.
Once you open the visibility layers modal, you can check the box that says "Show Deployment" and display the grid over your map. You can choose from a 10 x 10 meter grid, or a 30 x 30 feet grid.