Can I create a Salesforce form that enables customers to pay online?

Sure you can.
FormTitan is built like a Lego, containing powerful features you can use together in different ways to create your own custom form. 
Salesforce integration and Payment integration are one of the many examples for two features that work seamlessly together.

All you have to do is:
- start off by creating your form. Simply use drag & drop to add fields.
- Add a Payment integration to the form to collect payments online. Choose your preferred payment processing service and fill in the required parameters. Read how to add a payment integration
- Set a Salesforce Push integration that writes the information entered in the form in the relevant SF objects.
- In the Push settings: Turn on the "Use for payment integration" checkbox to connect both features and have your payment info pushed to Salesforce along with the rest of the data from the form. Learn how to get your payment information pushed to Salesforce