When using the register parameter, the output is almost always returned as JSON. Here is an example of using the register parameter with the find module. The debug module can be used to print the JSON.

---
- hosts: localhost
  tasks:
  - find:
      paths: /tmp
    register: out

  - debug:
      var: out
...

Which should return JSON like this.

ok: [localhost] => {
    "out": {
        "changed": false,
        "examined": 1,
        "failed": false,
        "files": [],
        "matched": 0,
        "msg": ""
    }
}

Let's say you only want to print the "matched" key.

---
- hosts: localhost
  tasks:
  - find:
      paths: /tmp
    register: out

  - debug:
      var: out.matched
...

Which should return something like this.

ok: [server1.example.com] => {
    out.matched: 0
}

Let's say the following JSON is returned. Notice here that the "files" key is a list, as indicated by the [ ] brackets.

ok: [server1.example.com] => {
    "out": {
        "files": [
            {
              "path": "/tmp/foo.txt",
           }
            {
              "path": "/tmp/bar.txt",
           }
        ],
    }
}

One option is to do something like this. Index 0 is used to enter the first "files" key. If there were another "files" key, then index 1 would be used for the following files key.

- debug:
    msg: "{{ out.files[0].path}}"

Or you could loop over the files array.

- debug:
    msg: "{{ item.path }}"
  with_items: "{{ out.files }}"

Which should return something like this.

ok: [server1.example.com] => {
    "msg": "/tmp/foo.txt"
}

ok: [server1.example.com] => {
    "msg": "/tmp/bar.txt"
}

Or like this.

- debug:
    msg: "{{ items }}"
  vars:
    items: "{{ out.files | map(attribute='path') | list }}"

Which should return something like this.

ok: [server1.example.com] => {
    "msg": [
        "/tmp/foo.txt",
        "/tmp/bar.txt"
    ]
}

loop / with_items

Let's say you are using the loop or with_items parameter.

- find:
    paths: /tmp
  with_items: [ foo, bar ]
  register: out

In this scenario, the JSON that is returned will begin with the "results" array and the "item" key.

ok: [server1.example.com] => {
    "out": {
        "results": [
            "item": "foo",
            "files": [
                {
                  "path": "/tmp/foo.txt",
               }
                {
                  "path": "/tmp/bar.txt",
               }
            ],
            "item": "bar",
            "files": [
                {
                  "path": "/tmp/foo.txt",
               }
                {
                  "path": "/tmp/bar.txt",
               }
            ]
        ]
    }
}

index_of

Or, the index_of module can be used to get the index number of an element in a list/array, to avoid looping through each element in the array, which can be useful in reducing the amount of output returned when looping through a large list.

---
- hosts: localhost
  gather_facts: false
  vars:
    fruit:
     - apple
     - banana
     - orange
     - grapes
  tasks:
  - debug:
      msg: "banana index number = {{ lookup('ansible.utils.index_of', fruit, 'regex', 'banana') }}"
...

Running this playbook should return the following.

ok: [localhost] => {
    "msg": "banana index number = 1"
}