Typically, the shell, command, or script modules are used to invoke a command on a managed node (e.g. target systems). /usr/bin/python needs to exist on the managed node to use these modules. If Python does not exist, the raw module can be used instead. 

The ansible-doc command command can be used to show the Ansible documention on the command module.

In this example, the ps command will be invoked on the managed nodes.

- name: ps command
  command: ps

The playbook can then be executed using this command.

ansible-playbook playbook.yml

The following should be produced.

TASK [ps command]
changed: [server1.example.com]

By default, no stdout is printed. The debug module can be used to print output to the console.

By default, Ansible performs tasks on managed node. The connection, delegate_to, or local_action modules/parameters can be used to run the task on the control node (that's your Ansible server).