function isset() checks whether variable is set or not and return boolean true or false.
You can use below code :

if (! (isset($_POST['name']) && isset($_POST['description']))) {
    http_response_code(422);
    echo 'name and description are required.';
    exit;
}

$name = $_POST['name'];
$description = $_POST['description'];

I suggest you to try to install guzzle.
http://docs.guzzlephp.org/en/stable/quickstart.html

To do a request to your api would be simple like

use GuzzleHttpClient;

$client = new Client();
$response = $client->post('adsf', [
    'auth' => ['username', 'password'], // basic auth
    // sending data via form request
    'form_params' => [
        'name' => 'Some name',
        'description' => 'Some description'
    ]
]);
var_dump($response->getBody());
var_dump($response->getStatusCode());

I’m new to PHP, and I’m developing a simple client for one of my subjects in college. The main goal of this client, is to do CRUD into a JAVA API. After a little research, I saw that for simple clients like this one, people use CURL. I have never worked with curl and I don’t know if I’m doing something wrong. When I submit my form it doesn’t appear any error, but when I open postman I see that my data was not posted successfully.
If anyone could help me, I would be grateful!

HTML FORM:

<form class="form" action="createActivity.php">
        <label for="name" class="labelActivityName"><b>Name</b></label>
        <input type="text" id="name" placeholder="Name" name="name">

        <label for="description" class="labelActivityDescription"><b>Description</b></label>
        <textarea id="description" placeholder="Description..." name="description"></textarea>

        <button type="submit"><b>Submit</b></button>
</form>

PHP CURL:

$url = "http://localhost:8080/myapi/actvities";

    $username = 'user';
    $password = 'user123';

    $name = (isset($_POST['name']));
    $description = (isset($_POST['description']));

    $fields = array(
        'name' => $name,
        'description' => $description
    );

    $client = curl_init();
    curl_setopt($client, CURLOPT_URL, $url);
    curl_setopt($client, CURLOPT_RETURNTRANSFER,1);
    curl_setopt($client, CURLOPT_HTTPAUTH, CURLAUTH_BASIC);
    curl_setopt($client, CURLOPT_USERPWD, "$username:$password");
    curl_setopt($client, CURLOPT_POST, 1);
    curl_setopt($client, CURLOPT_POSTFIELDS, $fields);

    $response = curl_exec($client);
    curl_close($client);