1. Top competitors
The first block lists the strongest competitors. For each domain you see the shared keywords, the number of top-10 rankings and the estimated traffic per month. That shows you who you are actually up against in terms of content. This does not always match the competitors you know.
2. Keyword gap
The second block presents the keyword gap against the closest competitor. For each keyword you see their position, the search volume, the difficulty (0 to 100, how hard the jump into the organic top 10 is, see SEO & performance) and how well your page covers the topic.
When no data comes back
Two messages are not errors: there is no ranking data for the domain yet, in which case it is probably new or not indexed. Or no keyword gap was found, which means you already cover this market well.