How do you run a playbook, and how do you read its output?

Run ansible-playbook <file>.yml on the control node. The output shows a PLAY header, then a TASK header per task with one status line per host (ok, changed, failed...), and ends with a PLAY RECAP that counts the outcomes per host.

$ ansible-playbook webserver.yml

PLAY [play to setup web server] ***************************

TASK [Gathering Facts] ************************************
ok: [servera.lab.example.com]

TASK [latest httpd version installed] *********************
changed: [servera.lab.example.com]

PLAY RECAP ************************************************
servera.lab.example.com : ok=2  changed=1  unreachable=0  failed=0

How to read it:

• PLAY [name] and TASK [name] print the name: values you wrote, which is why naming tasks well pays off.
• Gathering Facts is an automatic first task: Ansible collects information about each host (OS, IPs, interpreter) before your tasks run.
• ok = already in the desired state, nothing done. changed = Ansible modified something. failed = the task errored. unreachable = Ansible couldn't connect.
• PLAY RECAP is the summary per host. In the recap, ok counts all successful tasks, including the changed ones: here 2 ok, of which 1 changed.

The task name "latest httpd version installed" uses state: latest, which upgrades when a newer version exists; present would only install if missing.

Go deeper:

• ansible-playbook command reference (official docs) — options such as --limit, --check, -v.
• Ansible playbooks: running playbooks (official docs) — what happens during a run.