When you create a post, you'll see options above the text field that allow you to bold, italicize, etc. In the bottom row, you'll see a YouTube icon. Click on that, and a pop-up will appear where you can paste the URL of the video. The URL of the video can be found to the right of the video in YouTube (do not select the embed URL - just the plain URL.)
You can only embed videos from YouTube - Google video, etc. will not embed.
If you have the beta editor selected in your ST settings, you will not be able to embed videos in your post.
Feel free to practice posting videos in this thread, and let me know if you have any questions
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"Fashion can be bought. Style one must possess." ~ Edna Woolman Chase