Create Add-ons by going to Manage --> Add-ons.
Click New Category - if you need one - name it and click Save.
Click New Add-on, name it, fill in the description and assign to a category.
Pricing can be a flat rate, per hour or per day.
Enter the maximum quantity per booking and select taxable or not.
In the Advanced section, select:
Whether or not to multiply the price per add-on by the number of units if the package is priced per unit.
Whether or not this add-on extends the booking length.
Whether or not this add-on requires lead time.
Whether or not to display this add-on in your add-on gallery widget.
In the Images and Videos section, you can upload an image or select from your media library.
In the Packages section, select the packages that this add-on can be applied to. By default, new add-ons apply to all packages.