Moulds are silicone templates for all kinds of shapes. You fill them with a medium like clay, modeling material, or resin and the appliques harden. You attach them to surfaces for a unique design. I love using them on furniture and decor to add details to my designs. I prefer to use fast cast resin. It comes in 2 parts and you mix them in equal parts then pour it into the mould. It hardens within 10 to 15 minutes and turns white. You pop them out of the mould and can attach straight away or paint them first and then attach. It is pliable for a short time after it hardens. This makes it convenient for attaching on curved surfaces or anything uneven. You can also heat the resin moulds to soften them and make them pliable again.
You can use many types of adhesive to attach them. I like using e6000 as it is durable and dries clear. There are many industrial strength adhesives available. Try them and decide which is your favorite. I tape the mould in place until the glue has had time to dry. The weight of the appliques causes them to slide down. If you are applying on a flat surface level to the ground you don’t need to but if it’s upright it’s best to do so. It also ensures the applique remains flush to the surface without any gaps on the sides of it. Experiment with your favorite casting medium to achieve your preferred look. Clay tends to crack and shrink as it dries. Resin does not shrink or crack. Depending on what you are hoping to achieve you will want to use a certain product that has the characteristics you like.