First of all i created the symfony file through the following cmd :
php -r "file_put_contents('symfony', file_get_contents('https://symfony.com/installer'));"
After that, i performed the following command to create a symfony project :
php symfony new my_project 2.8
The result :
[GuzzleHttp\Exception\RequestException] cURL error 60: SSL certificate problem: unable to get local issuer certificate
So, is there a solution to this problem ?