Display a message after a client has made an order. How can I accomplish that?

My second question is I want the form to display a message after a client has made an order. How can I accomplish that?

You can simply setup a "Thank You" page on your form. Here's a guide that you can refer to: https://www.jotform.com/help/211-Setting-Up-the-Thank-You-Page 

You can either have a custom message page or you can redirect it to another link.

I hope that helps.