Have a helper hold a loop in the stick. If your stick looks like it is going to break when you bend it like this, either find a more pliable one, or soak your stick in water for a few hours. Make sure your net bag will stretch over the loop.
Firmly wrap string at the bottom of the loop, to hold it in place on the handle, and knot.
Now stretch the net bag over the inside of the loop. Let the edge hang over the outside of the loop. Starting near the handle, sew on the net bag using the string and a running stitch. If you have a large-eyed needle, like the kind knitters use, this step will go much more easily.
Knot the ends at the bottom of the loop and trim.
Now catch something and have a good look at it! Don't try to catch insects which sting. And be gentle! If you want to learn about what kind of bugs make good pets, read the book "Pet Bugs: A Kid's Guide to Catching and Keeping Touchable Insects," by Sally Kneidel. It is a wonderful book. The description of the jumping spider is particularly memorable and funny.