A couple of ground rules for great cupcake and muffin results!
1. Always (and I mean always!) use a metal cupcake pan. Your muffins will look much nicer and are easier to work with. The pan causes the cake to rise upwards, rather than outwards, and the paper liners make the cakes easier to handle and transport.
Besides, paper liners come in all colours, sizes and patterns, for every conceivable event!
2. When dividing the batter between the liners, the easiest approach is filling the batter into a plastic bag, tie a knot, cut a corner, and fill!
3: Cupcakes can be decorated with frosting or icing. Icing is made of powdered sugar and liquid, for example water, coffee, lemon juice, booze or what you like. Frosting is usually based on butter, beaten with powdered sugar, and mixed with a little liquid. Frosting can also be made out of cream cheese.
4. Frosting can be spread on the cupcakes with a piping bag (perhaps using a nozzle) or with a knife/spatula. For a thick coat of frosting, I would use a piping bag, but for a thin layer a knife is easier to handle.
5. If you like a lot of frosting on your cupcakes, an idea is to make mini cupcakes, so they can be eaten in one mouthful. Otherwise it can get too much with a lot of frosting.