After Epochs are added to a study, next step is to add an arm to each of those epochs. To add an Arm to an Epoch, select the desired Epoch from tree structure

A screen appears where you can edit Label of the selected epoch and add Arms to it. The screen is instantiated with one row. Enter Label for the arm and select Submit

To add more arms, select Add more button and enter Labels for the arms and select Submit.

Once you select Submit, arm is added to the epoch and is displayed in the tree structure.