How do you upload video(s) from your computer to a WordPress.org blog you ask? You could upload your video(s) to your Youtube account and then embed your Youtube video in a blog post. Also, you could upload small videos directly to a blog post.
I just tried it on one of my blog's and I received a 2 MB limit message. If you have access to your php.ini file on your web host, then you can increase this value to greater than 2 MB. Youtube video's are limited to eleven hours and 128GB each.
There are other free video sites that you can use. Vimeo, LiveLeaks, etc. allow you to upload videos, which can then become embedded in a WordPress blog post. One advantage of uploading your video files to a video hosting site is disk space.
You can use up disk space quite quickly if you upload your video files to your own web server or web host.