How can I let users to specify custom quantities in an order form?

Hello,

I am trying to create a simple form in which those filling out the form can specify how many tickets they want to purchase at $10 a person and then the total is calculated for them and they can pay with PayPal.

Thanks!

Please check the following guide: https://www.jotform.com/help/47-Order-Form-Basics
What you can do is add a PayPal payment tool in your form and enable the custom quantity property for the ticket so the quantity value can be entered manually.

Please take a look at this demo form: http://form.jotformpro.com/form/43375993814972 and let us know if this is what you're looking for. If it is, feel free to clone it to your account to check it further.

Thanks.

By the way, I forgot to suggest that you also take a look at this guide: http://www.jotform.com/help/225-How-to-add-options-to-Payment-Forms in which you can see how to add the custom quantity (check section II) to your payment tool.