Recently YouTube started the Shorts on their platform. Right now it's still a test and they've opened up the Shorts function for people in India and some random chosen people. In order to use it you should use the app on your phone and click on the camera as you would to upload a video. Here you will find the option to upload a Short if you have it.
If you don't have the option yet you can still post a Short by uploading a video the way you normally would and putting the word #Shorts in the description. It can take a few days before YouTube can pick up the video for Shorts, but it is a way around using the actual Shorts function.
In order to post a short you have to make sure your video is vertical and is no longer than 1 minute long. Now you might want to consider that your Shorts will end up with your regular videos and if your Shorts are very different from your regular content it might not be appreciated by your subscribers.
That being said, for a newer channel that is trying to grow it can be very helpful. I tested the shorts on a channel with less than 1000 subscribers that normally gets between 10 to 50 views on a video. I posted 2 Shorts with a week in between, the first one had almost 500 views in 4 days and the second over 600 views in 3 days. So there were quite a bit more people to view the Shorts than the regular videos.
On top of that the first video brought in 3 new subscribers and the second one a whopping 7 new subscribers. Now this might not seem much, but for a growing channel, trying to get to 1000 subscribers this could actually make a big difference.
Now the question is of course how this will continue to work when there will me more and more people making Shorts, but right now it seems that there could be a great opportunity if your channel allows it and you have the right content for it, to have a little growth spurt in your channel by using #Shorts.