newbie aid?

Hello. I’d like to build a web application. I’ve collected all the data I need from my client. Now I need to use BPMN. This is all new to me obviously. I didn’t know tech like this existed. I’ve been looking for days now on and off as to how to proceed.
NaturalONE didnt work for me. Some prbs with installation couldnt get anys upport. I went to ARIS but the only thing I can download was the free express one.
I am learning how to do BPMN but I don’t know how to do the rules.

So I was hoping that someone here would help me once and for all figure this out.
Currently all I want to do is BPMN + business rules.
To do BPM I use the diagram model available in express and sgtart building. I was going to use business process model but I saw BPM model so i figured this is right. RIGHT?
What about the rules? How do I create them? I read that part of ARIS platform had a business process designer and a uml designer. They both mentioned sometihng about producing executable code or application execution. I’m still lost. So plz help. If you have any detailed tutorials about diff scenarios regarding BPM AND how to derive or create business rules i’d really appreciate it.