What is the purpose of the pm.sendRequest() in Postman and how do you use it?

pm.sendRequest(requestObject, callback);

// requestObject can be:
// 1. A URL string: "https://api.example.com/data"
// 2. A full request object with method, headers, body

pm.sendRequest({
    url: pm.environment.get("base_url") + "/auth/login",
    method: "POST",
    header: {
        "Content-Type": "application/json"
    },
    body: {
        mode: "raw",
        raw: JSON.stringify({
            username: pm.environment.get("username"),
            password: pm.environment.get("password")
        })
    }
}, function (err, response) {
    if (err) {
        console.error("Login failed:", err);
        return;
    }

    const token = response.json().access_token;
    pm.environment.set("auth_token", token);
    console.log("Token fetched successfully");
});

// Now in the main request Headers:
// Authorization: Bearer {{auth_token}}

// Pre-request Script — create a user to test getting them
pm.sendRequest({
    url: pm.environment.get("base_url") + "/api/users",
    method: "POST",
    header: {
        "Content-Type": "application/json",
        "Authorization": "Bearer " + pm.environment.get("admin_token")
    },
    body: {
        mode: "raw",
        raw: JSON.stringify({
            name: "Test User " + Date.now(),
            email: "test_" + Date.now() + "@example.com"
        })
    }
}, function (err, res) {
    const newUserId = res.json().id;
    pm.environment.set("created_user_id", newUserId);
    console.log("Created test user with ID:", newUserId);
});

// Main request: GET {{base_url}}/api/users/{{created_user_id}}

// Tests tab — delete test data after validation
pm.test("User created successfully", function () {
    pm.response.to.have.status(201);
});

// Cleanup
const userId = pm.response.json().id;
pm.sendRequest({
    url: pm.environment.get("base_url") + "/api/users/" + userId,
    method: "DELETE",
    header: { "Authorization": "Bearer " + pm.environment.get("auth_token") }
}, function (err, res) {
    console.log("Cleanup: deleted user " + userId + ", status: " + res.code);
});