These are called CSS-s. They are backgrounds for you den that sometimes come with really cool mouses! They have free ones and non-free ones. CSS-s making is coding and its not easy if your looking to buy one thats 5 or more gb. It is best newbies use free ones from here Clicky Those are all free CSS-s!

"How do I paste them in my den" once you have clicked on the css provided you like your search bar has the link, copy and paste that link in your den! And boom! some may say remove * and if you don't it might not work! Now if your already taken to a link and its Infront of you just copy and paste that!