Understanding is constructing meaning from different types of functions either written or graphic. A variety of tools exist that allow students to comment on web pages. The student is developing understanding simply by commenting on the pages.
For my student led lesson, I created a google doc that allowed for the exploration of three content curation sites: Pearltrees, Scoop.it!, and Storify. Students searched for information and summarized their findings relating to certain aspects of their respective curation site. By summarizing their findings and commenting on their site, they were developing a greater understanding of that content curation site.