How to assign a Delivery Server on GROUP?

Hello Twisted,
You guys are doing excellent job, can you please send me the manual of backend settings?, and please is there any way to set a delivery server on groups? I found a tag here " backend -> customers -> groups -> create new " name as assigned server: but its empty,how to set a delivery server here, so my all customers those are in specific group can use a same delivery server.

The backend is always changing and that's the reason why there's no guide for it just yet, but if you browse the forums you'll find info for almost every section you need to know.

To assign delivery servers for groups, you just have to create the delivery servers and make sure you don't assign then to customers, then create a customer group and from there you can select one or more of these newly created delivery servers.

Hello Twisted,
I've done what you said but after login from customer end my sending campaigns are still in "Pending-sending" status.
"customer -> servers -> delivery server -> empty" and I don't have any delivery server there, even I set delivery server on group, and that customer is belong to that group.