A material that you have on a miniature is more or less a bookmark where you stopped painting and what layers are still to do.
To assign materials to a miniature go to your Project, tap "manage" below the miniatures section, go to the miniature you would like to edit. In the miniature view you can add materials by tapping the + in the upper right corner. Choose the materials you would like on your miniature and press and "Add" in the upper right corner.If you don't have any materials yet, you are asked to create some first. By default the bookmark is set to the material and no layer! You can see this as the material status is "Not started". To change the layer you are currently painting, tap the material in the bookmarks view (you can see the name of the current miniature on the top) and long press & hold on a layer. This will bring up the context menu. Choose bookmark. You will see a small star on the right side that indicates the current layer of this miniature. If you go back you can see the progress changed.
There are 2 special cases:1. The First LayerIf the current bookmark is on the first layer AND you set the bookmark to this layer again you are asked if you like to reset the material to "Not started".2. The Last LayerIf you bookmark the last layer you are asked if you are done or not with this material. Bookmark any other layer and the status of the material is reset to "In Progress".
One thing to note: one miniature can only have one bookmark on the same material, so each time you set a new bookmark on the same miniature and material, the old one will be updated to the new one. This is because it would be very confusing to be on different stages on one material on one miniature and is therefore not supported.