When watching a YouTube video, you're likely to see a few annotations over the duration of it. Annotations are the little boxes that crop up here and there, acting as somewhat of a commentary over the video and adding a level of interaction with the viewer.

Though they can be annoying and rather distracting if done poorly, annotations can prove to be a massive boon for your YouTube channel, as they can go a long way to improving user engagement as well as the viewership of your channel by providing calls to action for your viewer base.

There are several ways in which they can be used in order to prove fruitful for your YouTube ventures. You can use them, to simply ask your viewers to 'Like' the video. These can also be used as an incentive, as some YouTubers tend to ask for a certain amount of likes before offering a reward for the viewers, such as bonus content. You can also provide links to videos, playlists and your/other channels, as well as a direct link for viewers to subscribe to your channel.

Annotations can be used to improve the viewer's overall experience. For example, if you've created a video where you're covering several topics/points, you can use annotations to create time stamps (create an annotation which links to that video, but by starting the video at a certain point), so that viewers can watch whichever part of the video they desire.

Another tactic that is used in order to increase the click-through rate and viewership of videos is to create some annotations for other videos towards the end of the video. This is usually accompanied by a graphic with a snippet of the video playing and the annotation created over it. Here's a perfect example of this, courtesy of Matthew Woodward:

At the very end of his video, he has created a graphic that contains snippets of previous posts and a subscription button, all of which have annotations with links to everything accompanied with them. If you've taken the time to create a video, take that slight amount of extra time to create something like this, as it has vast potential for channel growth, and gives viewers more incentive to stick around after watching one of your videos.

This transitions into my next point; the placement of your annotations. It's vitally important to avoid just spamming annotations all over the video, considering that most viewers will just remove all annotations. Make sure that your annotations aren't covering any of the content within the video or will be blocked off by any ads that have been placed on your video.