The easiest way to upload a video from your computer if the video is on your computer:

To put a video on your blog from a website, like YouTube, you can either embed the video, and the video will appear on your blog, or you can put a link to the video, and when someone clicks the link, they will leave your blog and go to the page where the video is.

To embed, follow the instructions on the picture.

To create a link, copy the URL from the web page you want to link to:

Highlight where you want the link:
then click the link button, as described in the window below
and paste the into the blank.

Then publish your post, and check it to make sure it works!