Created folders appear in your map list in the upper left corner.
There are 2 ways how to put map in a folder:
Already created maps:
click on the three dot icon under the map preview. (pic. 1) Then choose "Move to a folder" option. (pic. 2)
New maps:
Click on the Folder section in a map settings. (pic. 3) A folder list will appear on your screen. Move map to a folder you need. (pic. 4) If the folder you need does not exist, create a new one by clicking on the +New folder option.
pic. 1
pic. 2
pic. 3
pic. 4