Firstly, make sure you check out all the ways you can collect payments through the MightyForms and Stripe partnership:
Once you pick the best-fit payment field and start to build a Form, you'll see that each of the payment fields will ask you to specify an Email field from your form directly in the field's settings toolbar.
Make sure you add an email field to your form for your customers to fill out.
This way, each submission that includes a Stripe payment will automatically create a Customer in your Stripe based on the submitted email address.
Stripe Mapping - more customer data
For some business processes, you might need more customer details such as name, phone number, shipping address, etc. You can easily have them recorded using Form-to-Stripe mapping in the Integration section.
Simply pick fields that were earlier added to your form and then select related Stripe fields where you need data from submission to being recorded.
If a typical set of Stripe system fields is not enough for your case, you can even add additional fields using the Custom section. Name a new field you'd like to add to Stripe Customer overview page and pick up a form field where we should take data from.