Few Question About Routers and Dns .?!

hello .

what hackers do exactly with hacked routers , i heard about hackers that compromise a lot of routers

i want to know how they have made a rogue dns server ?!?!! it's like dns spoof over wan .

i want a specific guide to make a rogue dns server (public) .?

what else can they do ?!

can we compromise a device connected to the router that we have access to . ?

(but we are not connected to it so mitm will not be available here .. )