Hey there, welcome, great job on initial assignments. As for masks, they are basically something you place on your layer to hide a part of it. You can use anything on the layer to “paint” what you want to hide - using brushes, text, shapes, etc and that part of the layer will disappear revealing what is behind it
For example, you make a figure and you want it to hold a prop. You make a prop on another layer on top of your figure and want to hide the part of the prop where the fingers overlap it. You can erase that part, but that’s destructive. A mask will just hide it using black or white to tell the program what to hide. Grays will make it slightly transparent
Cheers
