How can i make a custom content

Well, i'm not sure what you want to start with? You can start by making recolors of objects or cas items. There are several tutorials in the forum. HERE is the full index showing all the tutorials in this forum. Check it out, start with the basic tutorials, and if you have more questions about a project please ask.

 You will find in the tutorials a really well explained infomation to help you make the CC. If you decide for something in particular tell us and we can point you to a particular tutorial.

Ok. I'll point you to some tutorials that may be useful for you to read.

HERE about basic recolorig of a clothing item.
HERE about the Studio interface and recoloring cloth.
A video tutorial HERE

This tutorials are the basics to do. It will help you understand it more, after you manage that you can read more about to improve your CC by a more fully edit of that resources. You can find may tutorials in the forum as well.

After that you may want to experiment with meshes too. But you need the basic recolor information to start with that.