Omics data: How to interpret heatmap and dendrogram output?
The dendrogram summarize the information of a group of values and sort them according to the similarity they have. It can be applied to both, samples and features.

The dendrogram allows to visualize features that are more similar together, usually revealing patterns that wouldn't have been seen otherwise. 

In an article usually it is used something like: "we can see that X and Y are clustered together revealing that ... (they have something in common), while Z and A are clustered far"