A material can be created by pressing the yellow + button on the top right corner of the app, or pressing the Create button on the bottom when looking at your formulas. You just give a name, and optionally a description, stage, categories, max IFRA %, and recommended composition %. If you specify consisting items in the composition section, it will automatically become an accord.

If you typed the name of a material in a search field when browsing, and you couldn't find it, a yellow button will appear on the button starting with Create with name... Just press it, and the material you were looking for will automatically be created, and assigned to your formula.