In the COMPOSE mode of Blogger post editor there is a video upload icon which you can click to upload video. However, we have found that to be messy and if you want videos in your blog, it is far better to upload them to Youtube then embed into your blog.
After you have successfully uploaded a video to Youtube.com, then below the video click SHARE > EMBED to get the embed code. The code will look something like this (you don't need to understand the code in order to use it):
<iframe width="560" height="315" src="https://www.youtube.com/embed/HEVBWRzU5SA" frameborder="0" allowfullscreen></iframe>
Then if you want to embed the video into a blog post, then click the orange pencil icon to open the post editor. Note that you have to be in the HTML mode. Note also the width of the video above is 560px and this may be wider than your blog post column width. To change, click the SHOW MORE below, select CUSTOM SIZE
Click in width field and type a number suitable for your blog post column width then click in the HEIGHT field. The height will automatically be added such that the aspect ration is maintain so video wouldn't be distorted.
Dashboard > Layout > Template Designer > Adjust width
and you can see the sidebar width there (also total width - sidebar width = blog post column width)