Some are just stained with coloured inks and others are coloured free hand with felt tipped pens and then a sealant over them. I have covered others in fabric and stuck on pieces of old jewellery and sequins etc.
My current project is decorating some frames I got at IKEA. They are just plain wood and are 5 x 7 inches in size. Over the years I have collected lots of beads and stones and little plastic objects and have long been looking for a way to use them.
Sometimes I go to a place in Rotterdam where you can buy factory waste like little rubber thingies that look like drawing pins or sheets of tins or coloured threads........all sorts of stuff. Each time you go there is something different.