Question

What is a YAML file and how do we use it in Ansible?

Answer 1

YAML or files are like any formatted text file with few sets of rules just like JSON or XML. Ansible uses this syntax for playbooks as it is more readable than other formats.
An example of JSON vs YAML is:

{
 "object": {
"key": "value",
"array": [
  {
    "null_value": null
  },
  {
    "boolean": true
  },
  {
    "integer": 1
  },
  {
    "alias": "aliases are like variables"
  }
]
 }
}

---
object:
 key: value
 array:
 - null_value:
 - boolean: true
 - integer: 1
 - alias: aliases are like variables