CodeRunner questions can only be used in quizzes - create a new quiz and add to it the questions you have (I assume) added to the question bank.
Moodle "Lessons" have their own (very limited) built-in feedback questions, which can be used to direct the path the student takes through the lesson. Lessons can't use the much more general questions supported by the Quiz Question API. [And if you think this a weird restriction, join the club.]
We use quizzes instead of lessons for this reason. You can insert "Description" pseudo-questions (they are unmarked) into the quiz to create a sequence of interleaved information panels and questions, much like a lesson.