I don't understand how to create a route with Strapi 4

Thank you nitin_tejuja. I feel I am moving forwards… I just replaced POST with GET, because I am trying to get comments from my post. Still, I have a 404 error :

    "data": null,
    "error": {
        "status": 404,
        "name": "NotFoundError",
        "message": "Not Found",
        "details": {}
    }
}