What should I actually do when viewing an animal in a video? In addition to classify this animal on existing options, I must also add their comment using hashtags that animal?
I have observed that there are few videos (not "chimps" videos) that were added comments and I'm in doubt about doing it or not.
Comments are completely optional. If you feel the video would be better classified if a comment were added (e.g. #genet to distinguish it from other non-primates, or to note something interesting/funny about the video), then go ahead. However, the main classifications are the most important.
They also help fellow volunteers to find images with certain animals, and flag images as particularly interesting. But, yes, as @DataDroid said, only when you want to. Totally optional. đ