If you are not familiar with modules, check out Ansible - Getting Started with Modules.

The docker_network module can be used to create, update and remove a docker network. In this example, the foo-network Docker network will be created.

- name: create Docker network foo-network
  docker_network:
    name: foo-network

In this example, the subnet and default gateway are defined.

- name: create Docker network foo-network
  docker_network:
    name: foo-network
    ipam_options:
      subnet: '172.50.0.0/16'
      gateway: '172.50.0.1'