Inserting or "Embedding" YouTube Videos into Your Post
You can simply copy a YouTube address and paste it into your Post-Reply window as a plain link text so people can click on it to open YouTube and see the video.
Or... You can easily "embed" the video's "iframe" code into your post to make the video playable within your post (like the video embedded at the end of this post).
The following looks like a lot of steps but it's intuitive and easy to learn, and it's really just a couple of "copy and paste" steps.
Here's how!
HOW TO COPY the "iframe" embed code from a YouTube video and "embed" it in your post so that the video appears within your post. 
1. Open the video in YouTube.
a. Click the SHARE option.
b. Click either COPY or EMBED.
"Copy" will simply copy the video's URL to your clipboard which you can then paste in your post to create a plain link.
"Embed" will open up an option to get the video's "iframe" embed code. See the embed option below.
c. After clicking the Embed Tab, click COPY to copy the iframe Embed code.
You're now ready to paste the Video's "embed" code into your post
2. Click the INSERT MEDIA option on your Post-Reply Window Toolbar at Rotation.org.
3. Click the EMBED tab on the Insert Media window and paste the "iframe" code (which you copied from YouTube's share feature) into the field. Click "ok" and the video will now appear in your post!