If you wish to edit individual steps within an appointment, open the new appointment creation window and switch to Service step event at the top.
Here you can switch between Preparation, Post-processing, Break and Step:
Preparation & Post-processing: These are only shown in your calendar and do not affect the customer's appointment duration. The corresponding time cannot be booked by other customers.
Break: This is shown in your calendar as an available slot and can be booked by other customers.
Step: You can create and name as many steps as you require.
Hint: Make sure that the Preparation phase is always at the beginning and the Post-processing phase is always at the end.