Canva

Canva is a cloud-based graphic design platform that enables users to create visual content through an intuitive drag-and-drop interface. It provides ready-made templates, stock images, icons, fonts, and design tools for producing presentations, social media graphics, posters, videos, documents, websites, and marketing materials.

You can watch this beginner introduction to understant the basics: https://www.youtube.com/watch?v=Wz6LAD5A-7M

For more advanced features here's a full tutotial: https://www.youtube.com/watch?v=Dgha6qBtAwQ