Before you read this part, make sure that you already read the Videos article in the Slider Settings.
So in the following you can read how to embed Youtube videos into your layer:
First of all create a new slider or click on an existing one in the slider list for edit. Here select or create a layer where you would like to paste the video. If you get one, click on the HTML/ Video / Audio button under the Content tab. Please note that if you are not familiar with the UI of the Layer Slider you can read the other parts of the documentation first.
Youtube is one of the most popular video sharing pages over the internet, so you usually faced that you need to insert a video on your website. If you navigated to the proper area of the LS, now you need to select the video on Youtube. Under the video, click on the Share button, and then the embed button. Here you will see the embed code within an iframe tag. Under the code you can set additional settings, like related videos, size, and so on. If you finished with those ones, copy the code, and navigate back to the selected layer in the Layer Slider edit page. Then nothing else to do, just place the embed code into the textarea. After that the youtube video placed into your layer. Don't forget to save the slider.