The walkthrough videos address one concept each, using an example question that we feel represents the sort of skills the students need for that concept. We don't make one video per question (with over 30,000 questions in our database, that would take a while!), and instead use the videos to provide an example of how to solve a similar problem. The students can then take the example they saw in the video and use a similar strategy to solve the problem they are working on.
Some standards have multiple videos for students to watch, depending on the type of question and depth of the standard. We encourage students to watch these videos when they are having difficulty with a question (click on the play button icon to watch the videos at any moment).