Rolled fondant (adapted from this recipe)

750 g (6.25 cups, unsifted) confectioners sugar
75 ml (5 Tbsp.) water
2 tsp agar-agar powder
20 g  (1.5 Tbsp.) refined coconut oil
35 g ( 1,75 Tbsp.) sugar syrup (substitute corn syrup, maybe agave nectar works too)

Start by adding  the confectioners sugar (powdered sugar) to a mixing bowl. You don’t need to sift the sugar. Set aside. Combine water and  agar agar powder in a small saucepan and cook for one or two minutes until it turns into a jelly-like mass. Add sugar syrup until dissolved, remove from heat, add coconut oil and stir until the oil is melted and everything is well mixed. Let cool a bit.
Pour the mass into the mixing bowl filled with sugar and kneed with your hands until you get a smooth, marzipan like mass. Voilà, your fondant!

Now you can store it in an airtight container, bake some cakes, make a filling if you like and then start decorating:

If you want to work with the fondant, roll it out between two layers of plastic wrap like this:

You should try to always keep the fondant wrapped in plastic because it dries very fast. If it gets to dry while working with it, you can add a few drops of lemon juice. Also put some drops of lemon juice or water on the cupcake before you place the fondant there. I also added a few drops of food colouring.