Why submissions are pending? It says on the form "WAIT" and then I need manually complete payments.

Please wait means that the form is in the process of submitting the data, but since the form is integrated to Paypal, you will need to complete teh payment first before you will receive it through email and in the form submissions page. If you won't complete payment, the submission will be listed in your incomplete payment list. 

For incomplete payment, please check the following guides:

http://www.jotform.com/help/564-how-to-view-incomplete-payments-of-your-payment-forms/

http://www.jotform.com/help/272-Paypal-Incomplete-Payments-FAQ

Let us know if you have any further questions.

Thank you.