This is a great introductory site to cad programing and creation. Created by Autodesk, this site allows users to make 3D models and can be sent to a 3D printer. www.tinkercad.com
If you have mastered all that Tinkercad has to offer then you should try the next level with Onshape. This robust program allows users to design and engineer parts and products all on a browser. In addition is gives users online tutorials on best practices with the program.
Many times students want to edit or change an image for a project. Below are some sites that I find really user friendly with low prior knowledge needed for image editing.
This site gives individuals quick guides and tutorials when getting started with maker space creation. In addition, they have quick design challenges for all ability levels.