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

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. 

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

- name: ps command
  command: ps

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.

Arguments

The chdir argument can be used to change into a certain directory on the managed node before running the command.

- name: invoke example.sh
  command: example.sh
  args:
    chdir: /tmp

Let's say the creates parameter contains /tmp/foo.txt. If /tmp/foo.txt exists, the task will not be run. If /tmp/foo.txt does not exist, the task will be run.

- name: invoke example.sh
  command: example.sh
  args:
    creates: /tmp/foo.txt

Let's say the removes parameter contains /tmp/foo.txt. If /tmp/foo.txt exists, the task will be run. If /tmp/foo.txt does not exist, the task will not be run.

- name: invoke example.sh
  command: example.sh
  args:
    removes: /tmp/foo.txt