When you put together a video, you have two major outcomes you are looking for. The first is that people view that video, and do all the things associated with viewing it (commenting for engagement, sharing for visibility, etc.). The second is that they view other videos that you have put out, or other content you have produced on that and other websites. To make this happen, you need a call-to-action button.
When you apply it to your video, it is known as a Call to Action overlay. These are the little ads that come up at the bottom of the video player during your clip.
Making an overlay for your YouTube video is very simple.
Sign into your account where the video has been uploaded, or where you intend to upload the video.
Once a video has been successfully uploaded, go to the Account located at the top of your dashboard.
There should be a section titled My Videos, and under it, Uploaded Videos. Click this link and it will give you a thumbnail version of each clip that has been uploaded to your account. To each thumbnail will be an Edit button.
Editing the video will give you a Call to Action Overlay section with a series of text boxes. Fill these out with the necessary information, then click Save Changes.