EC2 dual-homed based on workload/role

Hi, This might be a basic question, but I can't understand on how topology would look like. "You can place a network interface on each of your web servers that connects to a mid-tier network where an application server resides. The application server can also be dual-homed to a backend network (subnet) where the database server resides. Instead of routing network packets through the dual-homed instances, each dual-homed instance receives and processes requests on the front end, initiates a connection to the backend, and then sends requests to the servers on the backend network." Source https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/scenarios-enis.html Please shade some light.

Thank you.