Question about payment submissions on each plan

It says a certain amount of payment is accepted for each plan.  Question is what does it mean ? If each form has a paypal payment associated, will each from submission count as one payment ?

It's called Payment Submissions.

When you form is integrated with any payment tools like Paypal, submissions with payments processed through your form are called Payment Submissions.

Yes, each submission is counted as one payment. It should be complete submissions with payments. Abandoned or incomplete payments won't be counted.