SAP Web Dispatcher installation Through gateway

Hi Expert,

I am stuck after the installation of Web Dispatcher. SAP Web Dispatcher is installed on SAProuter

Now We have ERP(Abap), CRM and SRM System connected to Gateway

Now the Idea is to connect to the gateway – through gateway we can connect to ERP, CRM and SRM systems for the corresponding Fiori apps.

I have a few Question and need help :

1. How will we connect the Web Dispatcher to the Gateway which in turn Connect to other System.
2. Why is Web Dispatcher needed when we have a gateway System.
3. Is there any configuration done on the Gateway System and the Other System (ERP, CRM and SRM).
4. Also Since our ERP System is an ABAP System, how can we access through URL.
5. Can Anybody Suggest me the best method for the Web Dispatcher configuration for this scenario.

Thanks & Regards,

Xherdan Romeo