Have you taken a look at our Report Designer video tutorials? They're a good starting point if you haven't dealt with Report Designer much. It's a fairly robust program, so it's not surprising if you don't know how to use it right off the bat.
The Generate Report action is an action in Method (not in Report Designer), that you can use on a screen (usually by clicking a button) to generate a report. We have a Help Center article about it here.
If this is something you don't wish to undertake yourself, or don't have the time to, you could always hire a member of our Professional Services team to do the customization for you. Let me know if that's the route you'd like to take and I'll have your account manager reach out to discuss.
Hope this helps.