I’m still figuring out how to operate a YouTube channel, but I’ll share what I know for the benefit of those who know even less than I do. I’d welcome suggestions for those who know more than I do!

I think it’s important to take the extra time to add captions. This isn’t just for the hard of hearing; it’s for the many millions of people around the world who can process printed English in a video (perhaps pausing the video at times) but can’t process spoken English (or can’t process it at speed). With a small investment of extra time, you can greatly increase the global accessibility of your video content.

How to upload a video to YouTube:
1) Go to YouTube.com
2) Log in to the desired channel. IMPORTANT: If you own more than one channel, switch over to the correct one now. You will not get a chance to change your mind later, and there is no way to move content from one channel to another, even if you own both.
3) Press the Upload icon near the upper right (it’s a horizontal line with an upward-pointing arrow above it).
4) … (I may add more steps later, once I get better at making use of the options YouTube offers).

How to add captions:
1) Go to YouTube.com
2) To the left of the YouTube icon, click on the drop-down menu.
3) Click on “My channel”
4) Switch to the correct channel.
5) Near the top of the page, click on “Video manager”.
6) Find the video you want to work with, and click on the word “Edit” to the right of the thumbnail.
7) Near the top of the window, click on “Subtitles/CC”.
8) Click on the blue banner that says “Add new subtitles or CC”.
9) If your language is English, click on “English”. (I’m not sure what to do for non-English-language videos.)
10) You now have a choice. If you want the first draft of the captions to be created by YouTube, I think you should select “Create new subtitles or CC” (that’s not the option I use, so I’m not sure). I always create a transcript, so I select “Transcribe and auto-sync”.
11) In the box marked “Type what’s spoken here”, enter a transcript of all the spoken words in the video.
12) Click “Set timings”.
13) Wait.
14) After some suitable amount of time (depending on how long the video is), click on “English (setting timings…)” 
15) You will now see the CC editing screen. In the upper right, you’ll see the video with captions. Below that you’ll see a time-line that shows how the captions change over time. At the left you’ll see boxes containing the captions; you can edit the text here and also adjust the timings. When you edit timings, be sure not to create captions that overlap in time, because YouTube will override them. That is, if you want caption X to end sooner and caption Y to start sooner, change the end-time for caption X first; but if you want caption X to end later and caption Y to start later, change the start-time for caption Y first.  To delete a caption entirely, just click on the “x” at the upper right of the caption. NOTE: If there’s a bad break in a caption, don’t delete the line break, because there’ll be no way to add it back; just add or delete words before and after the line break as needed.
16) Click on “Publish”.