Go to 'Registrations' > 'Registration Forms' and click on '+' to create a new form.
Select a form that suits your business model or is the closest to the service that you provide. You can customise most fields, hence do not worry as you can make any changes later on if required.
Now that you've picked your registration form template, you can rename, edit or soft delete fields in the form. If you wish to add multiple custom fields, jump to 'Section 5 - Other (Custom Fields) where you can add multiple choice fields, short and long text fields etc.
If you want to maintain multiple registration forms, be sure to rename your forms accordingly for easy identification and editing later on.