This image shows a portion of the Networking Advanced variables on the Create stack, Configure variables page.
This is three of five.

On the left there are steps indicating the workflow:
1 Stack information
2 Configure variables, which is in bold font to indicate it is the current page.
3 Review

There are fields with sample text:
-Name of PIA/Elasticsearch Subnet
-CIDR of PIA/Elasticsearch Subnet
-Name of Generic Midtier Subnet
-CIDR of Generic Midtier Subnet
-Name of Bastion Subnet
-CIDR of Bastion Subnet