install.yml

---
- name: install ntp
  yum: pkg=ntp state=installed

main.yml

---
- include: "{{ action_ntp }}.yml"

play_ntp.yml

---
- hosts: someserver
  roles:
    - { role: ntp, action_ntp: "install" }

play_output

somehost# ansible-playbook ntp.yml -i hosts-test

PLAY [somehost] ***************************************************** 

GATHERING FACTS *************************************************************** 
ok: [somehost]

TASK: [install ntp] *********************************************************** 
ok: [somehost]

PLAY RECAP ******************************************************************** 
somehost         : ok=2    changed=0    unreachable=0    failed=0   

start.yml

---
- name: start ntp
  service: name=ntpd state=started