Drupal 11 requires PHP 8.3 or newer, a supported database, and a web server like Apache or Nginx. Drupal 12 is expected to bump these requirements slightly.
Supported databases include MySQL 8.0 or later, MariaDB 10.6 or later, PostgreSQL 16 or later, and SQLite for development only. You will also need Composer for managing dependencies.
On the server side, allow at least 256MB of PHP memory for most sites, with more for complex builds. Disk space depends on your codebase and uploads, but a few gigabytes is a reasonable starting point. For local development, DDEV or Lando handle all these requirements automatically, which saves a lot of configuration headache when you are starting out.