Hi Doris,
There are two ways to attempt this:
1. These resin pieces will need to be cast in a vertical mold. You will need to pour a little bit of resin on one side, then the other. It is almost impossible to get it even. (You can see from the picture that the stripes are pretty even.)
2. The resin is cast in layers, then machined to look like this. (Mostly likely the way it was done here too.) Someone likely used tools like a woodworking lathes to drill and polish the resin.