Annotations allow you to add to the video experience by layering text, links, and hotspots on your video. This helps add interest, increase engagement, and adds information to your video.
To add video annotation, follow the steps given here −
Sign into your YouTube account.
Go to the Video Manager within Creator Studio.
On the video you want to add annotation, click the down arrow to the right of the Edit button. Select Annotations.
Click the Add Annotation button on the right.
Click Apply Changes when you've completed your annotations.