The first step is to pull up the actual video in Youtube. Once you do, you'll see underneath it a button with the word "embed" ... go ahead and press it.
You'll get a couple options ... personally I just ignore them and power through. They're self-explanatory though. If you want to though, you can choose border color and video size (important if you have to worry about the layout on your page).
Now you can get the HTML code. You know how to copy and paste, right? Go ahead and copy it.
You need to find the "Edit HTML" or "View HTML" option while you're posting. It should be easy to find, and you've probably used it before. Go ahead and press it.
At this point, it's as simple as pasting the HTML code from Youtube right into the HTML for your blog post.
How are you building your webpage? If you're coding the HTML by hand, you already know what to do. If not, the process is very similar to the above.
Find the "View HTML" or "View Source" option. If you've never seen HTML code before, it will look a little strange, and you'll have to scroll around a bit to find the place to paste your code. It should be pretty simple though, and viola, you have a new skill.