A step-by-step breakdown of something is an explanation or instructions that are reduced to their most essential, simplistic or main points. You might have a step-by-step breakdown of accounts for example or a step-by-step breakdown of instructions to follow. Step-by-step breakdowns are usually used when there is a lot of information to take in or when the sequence of steps is important to follow.

1. Harry was taking ages explaining how the device works, so I had to tell him to just get on with it because I wasn't interested in a step-by-step breakdown!

1. Before I made my sales pitch, I asked for a step-by-step breakdown of the technology so that I could understand how it works at every level.

1. The new employee was given a rough overview of how the computer program worked when he was on-boarded, but he was still struggling to get to grips with it. What he really needed was an in depth, step-by-step breakdown.