1) Sign in to your account
2) Click the Create Payment Form button on the homepage
3) Title the form. You may want to say something like "Register"
4) Find the Amount section and choose Decided at Checkout. This will allow you to type in the amount on-the-fly.
5) Find the Frequency section and choose Decided at Checkout from the drop down menu. This will allow you to choose the frequency(one-time, monthly, quarterly, annually) as well as the start/recurring date, and duration/expiration, all on-the-fly as you're checking the payer out in-person.
6) Once you're finished with your form, click the Create Form button
7) On the Form Detail page, where you will arrive after clicking the Create Form button, click on the Preview button.
8) The checkout will should open in a new window or tab. Bookmark this page. You can now click on this bookmark anytime, enter the payer's payment information, their credit / debit card details, and check them out in-person.