If the inner part of the rim where the inner tube fits has spoke holes (like in the first photo), they must be covered by a rim tape (photo 2), usually rubber, cloth, or tough plastic, to protect the inner tube. Otherwise it may puncture. You probably already knew that; the tip is that if you don't have rim tape then a good solution is to use electrical tape (photo 3). Use around 3 layers and it should do you a good job.
applying electrical tape
