Woodworking skills. You know how to measure things. There are plenty of woodworking plans online that use the basic sizes of lumber sold in stores such as Home Depot.
The biggest stumbling block is then being able to make accurate cuts. Of course for someone who has fear of power tools and/or when living a nomadic life without the space or electricity for power tools then things like building a bed frame or cabinet can seem an impossibility that is too hard to overcome. But it is not. All it takes is a small investment in a few hand tools that make great work very possible. The saw system in this video is sold on Amazon. You need to also buy the saw that is made for use with the guide. It cuts very accurately and is not scary to use. I have one, I give it a 5 star rating. (The version I bought does allow for cutting at angles other than 90 and 45 degrees.) The cabinet doors in my trailer were all cut using it and the 90 degree joints are perfect. Even better it is small and light weight enough for taking along in Van Life in a small living space. No electricity required. No scary spinning saw blades and it is very quiet. The Japanese saws are so lovely to cut with, it does require a lot of physical effort.