Nesting markers is an important concept for pole loading. In order to load the pole correctly, photo inputs will need to be annotated and organized to accurately represent the build on the pole. The idea is pretty easy, but the order matters. To nest markers, simply drag your first marker to the next. When you see the box say "drop to add" you can let go and your markers will be nested.
It's helpful to have an example. We have a primary on a pin insulator on an crossarm. The arm is bolted to the pole, the insulator to the crossarm, and the wire attached to the insulator. You will have to start by dragging the primary wire onto the green insulator marker. You should see the "drop to add" section on the insulator marker when it's in position.
Once those markers are nested (the green input should surround the purple wire input) you can select that entire group and drag it onto the arm, with the same "drop to add" appearing when it's ready.
You can think of it like nesting dolls, where everytime you open one, a smaller doll is contained inside. If you were to put them back together, you would need to place the smallest one inside the next and close it. Then you can pick that up and place it in the next layer, with the inner most doll going with it.
Often with three phase primary systems you will need to repeat this to put everything on the arms. You will need your inputs to match and model what the real world assembly looks like.
If you ever need to "un-nest" markers, you can do so using the "pop-out" button. This is a good way roll horizontal builds from arms to vertical builds at adjacent poles. You can un-nest wires from insulators or insulator/wire groups from the arm.