You can gather a dozen acorns from any park or sidewalk around you or,
if you don’t have those where you live, you can order them online from places like Amazon.
First, if you are using whole acorns, remove the nut from the cap by twisting the latter with one hand, while holding the nut with the other.
Next, choose a preferred color of balls and simply glue each ball to an acorn cap using the glue.
Let out to dry and arrange.