Each project can have multiple miniatures and each miniature can have multiple materials from this project. You can just keep track of the miniatures in a project or connect your materials with the miniatures of a project.The best is to first create some materials you need and assign them to miniatures afterwards.
To create a miniature that belongs to a project go to your Project, tap "manage" below the miniatures section and tap the + in the upper right corner. You are pushed to the miniature view. In the upper portion of the screen you can edit a few settings of the miniature. You can also see the completition percentage of this miniature on the right side.
The miniature view consist out of 2 sections: "In Progress" and "Done"."In Progress" means there are still material layers to do and "Done" means there are no more material layers to do.
You can add a material to a miniature by taping the + in the upper right corner. This will bring up a list of all materials that are available in this project. Greyed materials are allready choosen for this miniature.