Click on the Tags tab from the Athena overview page.
To create a tag, press create new tag, then enter the tag name
To apply the tag, go to the playlist, channel, or screen that you wish to add the tag to.
Once in the Playlist, Channel, or Screen you wish to add the tag to, click on the tag bar. A drop-down menu will appear where you can select the tag you wish to apply.
Once you select the tag you wish to apply, press Save at the bottom of the screen.
To add a tag to a Video, the process is slightly different. Start by going to the Content tab from the Overview page.
From content go to the video you wish to add a tag to. Right-click and select Edit.
From Edit, you will see a line labeled Tags, click on the line and a drop-down menu with options will appear. Select the tag you wish to apply and press save.