Paint comes in tins or tubs, so if it's metal it would be a tin of paint or a can of paint. If it's plastic you might call it a tub of paint, these are the containers that paint comes in. You dip the roller in the paint and then you roll it up and down the wall. It applies an even layer of paint to the wall and it's very convenient for large surfaces. Masking tape is made of a sort of papery substance, usually a yellowy color,. Usually a pale yellow color, and it's tape that you can use to cover and protect parts which you don't want to paint.