Each of the timer editors have common properties. You can read more about these at Common Properties.
The custom timer simply performs a list of exercises in the order provided.
The list of exercises to be performed within the workout. Tapping on an item within the list will take you to the interval editor where you can update the values of the exercise.
Adding an Exercise
You can add a new exercise to the list by tapping the Add Exercise button at the bottom of the list.
Drag and Drop
You can move an exercise by tapping and holding the drag handle (≡) on the right of the row and then moving the exercise to the desired location.
Cut & Paste
It's possible to move many exercises at once using the cut & paste controls.
First copy the exercises by selecting the ones you want to move in the order you would like them to reappear. You do this by tapping the circle on the left of the row. The tap the Cut or Copy buttons from toolbar (you may need to close the keyboard to see this).
Next you can either paste the exercises at the bottom of the list by tapping the paste button from the toolbar. Or you may paste the exercises beneath a particular exercise by tapping and holding the exercise and then selecting the Paste option from the popup menu.
To delete an exercise you should first select the exercises you want to delete by tapping the circle on the left of the row. Then tap the Cut button from the toolbar (you may need to close the keyboard to see this).