How can i calculate the number of choices selected?

When ordering items, is there a way to have the last part of the survey tally the number of their selections?

Do you want to count the number of the selected checkboxes? That is possible, please follow these steps:

1) Add a value of "1" to each option in your checkboxes: https://www.jotform.com/help/301-How-to-Assign-Calculation-Value 

2) Then perform the calculation through the Form Calculation widget: https://www.jotform.com/help/259-How-to-Perform-Form-Calculation-Using-a-Widget 

Let us know if you need more help, we will be glad to assist you.