To get started wth adding your first explainer, click on the outer borders of any of your sections, as shown below, then click on the Add Video/Audio Explainer button.
In the upper left, you'll have the option to upload files directly from your computer. Below, you have the option to record a new video, and lastly, to record audio.
Recording audio and video directly is as simple as clicking on the respective option on the left, then clicking on the blue Record button.
Once you're finished, click the Stop button.
You will see the explainer you just created. Ensure you click the Upload button or your explainer will not be uploaded and you will need to do it again.
Once added, you will see a symbol near the upper-left corner of the section showing whether there is an Explainer attached. The panel on the right will let you delete an existing explainer or replace it with a different one.
When viewing a Studio document with explainers, Learners will see an icon on the upper-left corner, with the controls and the the video (if applicable) showing in the upper-right.