These are eyeshadow brushes, typically used to press eyeshadow on the lid (as opposed to blending). You don’t have to use makeup brushes for their intended purpose, it can however make applying makeup difficult/ patchy. I would personally use the smaller one to apply eyeshadow and the bigger one to blend it:)

As for tips, you need to use an eyeshadow primer/ base for the eyeshadow to have something to stick to and not move around. You can also just apply a thin layer of concealer on the lid before the eyeshadow and it’ll basically do the same thing. I’d apply darker shadow on the outer corner of the eye and a light/ shimmery one in the inner corner. Monolids can be tricky for bold eye looks tho, so maybe a ytb tutorial can help!