How to use Iframes in a Post

The first thing that you have to do is go to Youtoube.

Next, you are going to choose a video that you want to show in your post.

For example, I am going to use the song "Roar" from Katy Perry.

When you select the video,you are going to click the button "Share". It is under the subscription button of the Youtube Channel. 

Now, three new options will appear. You have to click in "Embed". It is located in the middle of that three options.

An "Iframe code" is going to appear. For you to know, the violet marked square contains the "Iframe code".

The next thing you have to do, is to copy that code.

You are going back to your post, and click on the "HTML" button. (It is next to the "Compose" button, on the left side of the toolbar.)
If you click there, a large text (it is better to call that text "codes") is going to appear. Well, if you did not write to much in your post, before putting the Iframe, it is not going to be large.

Now, you have to paste the "Iframe code" at the bottom of the "HTML" section. (Specifically, where there is a free space).
Now go back to the "Compose" section, and (if you did it right) a video is going to appear there.

And that's how you use Iframes in a post.