Hi, Jalus1 --

There may be more than one way to put a YouTube video in a Journal post.  This is the way I know:

On your profile page, from the blue column on the left side of the page, click Journal.

From the selections that then open up, click Add Journal Post to open up a post composition screen.  If you think you'll want to type some text above your video, do it now or at least create some lines (by doing returns) so you have room to type something after you've put the video in your post.

Then, from the tool bar in the grey area at the top of the message composition screen, click on the second-to-the-last icon in the bottom row (it looks kind of like a few frames of videotape or film, and it's next to the spell-check icon).  This is the Insert/edit embedded media icon.

In the upper area of the box that opens up when you click that icon, select "Flash" in the rectangle next to Type ("Flash" may already appear as the choice there, which is fine).  In the rectangle next to File/URL, paste in the URL of the video.  Once you do both those things, the video will appear.

Once the video appears, click the Insert button at the bottom left, below the video.  This gets you back to your post composition screen.

You won't see the video in your post composition screen yet; you'll see a big yellow box outlined in red with a gizmo (highly technical term :-) in the middle of it.  That's OK. 

If you want to type some text below the video, do it at this point; do a return at the bottom right corner of the video to get to a line where you can start typing. 

When you get your post the way you want it in terms of whatever combination of text and video you want -- or if you just want the video only -- (and you've given your post a title and selected your entry status) click Preview Post to actually see your video and the entirety of your post. 

If you like what you see, click Submit Post to post it.  If you want to futz some more with it, click Make Changes, get it all pretty the way you want it, and then click Submit Post (or Save Post).

And ... voilà! ... you have a Journal post with a YouTube video

If any of the foregoing isn't clear, just ask some clarifying questions here.