I created an account after clicking the non-profit link

I created the form I needed, too, using the free account.  Worked great.  I want to upgrade, but I don't know how to get the non-profit discount.  Also, not sure I really understand what some things mean: in the first block it talks about "receive payments." Does this mean that this is the number of people who can use your account to pay their fees? So, if it says 10, then only 10 people can donate or pay fees? Thanks.

Please use this link to apply for non-profit discount https://www.jotform.com/nonprofit/pricing/

As to your other question:

...about "receive payments." 

Submission payments refers to submissions using your form that include payments.

Example if you are using PayPal payment integration in your form, the submission will incur payment transaction via PayPal. 

The payment will be counted as Submission Payment (receive payment) in your account usage limits.

User guide: Understanding Your Account Usage and Limits

Let us know if you need further assistance.