Everybody knows the joke about the office intern who mostly makes coffee for people and copies and carries papers around because they're lacking the skills and the experience and knowledge about the specific company to do any real work. And nobody at the company wants to spend the time to teach them.
Here's a proposed improvement to that situation: to train your intern just let them become your shadow. Don't let them do anything. Just let the watch and hear everything. There should be some occasional explaining, but not too much and always making use of the context to keep it short. If you keep your intern that way, without any expectations to accomplish anything except for learning and understanding, they will soon become helpful with real work tasks. For example, one great use for an intern trained in this way is as a discussion partner when you need to verbalize some thoughts in order to think them more effectively. Maybe the intern won't be able to contribute anything to the discussion. But it will still help you think. And it will help them learn.
Even when your intern will be able to do real work by themselves, it will be very helpful to keep them shadowing you or someone else regularly. To learn new things. To keep up to date with the progress of the project. To be right there when the context enable to teach an important lesson with very few words.
Let there be more shadow internships and less interns sitting in corners working on small independent projects!