Some properties have mandatory fees associated with them. In some areas of the country it is common to charge a cleaning fee. In other areas of the country they charge booking fees. For one of my properties I charge a "Towel Service" fee. Mandatory fees are setup under the same "Taxes, Fees and Deposits" tab in the setup area for each property. All fees can be made tax exempt. Please consult your local taxing authorities to determine whether or not is necessary to tax your fee offerings.
Optional fees are really not fees at all. They are called ancillary service offerings and are setup under a separate "Services" tab in the property setup area. More on the revenue generating power of ancillary services can be found later in this tutorial.