How do I view and customise reports?

Also, how do I view and customise reports?

Since you never mentioned which specific report you're referring to, I'll just list a compendium of guides where you can see all the reports in detail and how to customize them.

Complete guide: How-To-Create-Form-Reports-in-JotForm

The guide above lists all the available reports and each will link to another guide tackling them separately.