Can someone help me and tell me how to get this design?

This looks to me like buttercream piping. To get that design use a circle cutter in your desired size make rows of circle imprints lightly into the icing and over lap them.

Then pipe over top. If you look carefully at the design it is just overlapping circles. I think the hard part is keeping the overlapping portion even.

Good luck, looks like a great project. Have fun with it.