I'm a student working an internship at a larger company, writing small business apps in C#. I've noticed that I don't comment my code as I write it. Rather, I comment my code when I'm in the debugging stage of development. As I'm tracking down bugs, I'll run across a block that makes me think "hmm...that might confuse someone in the future. I'd better comment that", and I'll add the appropriate comments. All of my comments are done this way.

Is this an appropriate way of commenting? Should comments be written as the code is written? Or does it really matter when the comments are written, as long as they adequately explain why this block is used?