To add closed captions to your videos, first go to Products:
Next, click on the product where your videos are.
Click the three dots to the right of video and then click "Manage captions".
From there, all you'll need to do is to add the *.srt file format and you're good to go:
The captions must be in *.srt format.
A couple notes:
- YouTube automatically generates these caption files for you and they can be downloaded from your YouTube dashboard.
- To view the captions, you have to click the little “CC” button in the lower-right corner when playing a video.