This assumes you have installed Ansible, are familiar with the ansible-playbook command and have created a playbook .yml or .yaml file.

The -l or --limit= options can be used to limit a task to be performed against certain target servers.  For example, let's say your inventory.yml file that contains the target hosts contains the following.

all:
  children:
    windows:
      hosts:
        server1.example.com:
        server2.example.com:
    linux:
      hosts:
        server3.example.com:
        server4.example.com:

In this example, the following command could be used to target only server1.example.com.

ansible-playbook playbook.yml -i inventory.yml --limit=server1.example.com

play_hosts can be used to store the server in a variable.