...is a thankfully simple process. With your project open in iMovie, select Share -> YouTube. Add your YouTube account name (you must open an account on YouTube in order to post), and your password. Select a category, and then give your video a title and - if you like - description. This is not an appropriate place for your summary description, however. Your summary should be posted underneath the video on your blog (see below, for example).
Be sure to select either Large or HD as the size for your video (preferably HD, unless you shot your video on a camera without this capability). Once you've posted your video to YouTube, it will be available on the site, although this can sometimes take several minutes to several hours depending on how busy the server is. DO NOT LEAVE THIS TO THE LAST MINUTE.
Once you are logged into YouTube, under your account name, select My Videos, then click on the title of your video. Your video will open and play in a viewing window on YouTube. Notice the box below containing both URL and Embed html codes. Be sure to select the customize icon to the right of the Embed code. Type in a width of 400. The height will be determined automatically. This will ensure that the Blogger window has enough room to show your video and that it will upload quickly. Keep the rest of the boxes unchecked. Please also ensure that your video is not set to "private" as this can cause viewing problems.
Now, highlight/select all of the code in the Embed box and select Copy. Then simply create a New Post on your blog, and paste the code into the text box.
When composing your post, you will only see html code, but when you preview or publish your post, you will see the embedded video file (see above). Your final task is to include the summary paragraphs for your video, which should be at the bottom of your post.