How can I create a section that adds up all products and gives 1 price depending on what they want?

You can use the Payment Integration to add products,add value and show the total purchase.

Guide:https://www.jotform.com/help/165-Setting-Up-Your-First-Order-Form

If you do not want to have payments in your form, you can use the Purchase Order Form.

Guide:https://www.jotform.com/help/460-How-to-Create-Payment-Form-with-Purchase-Order

Please give it a try and let us know your thoughts.

Thank you.