Can I just provide a Github account URL to them? This is the account that I'm about to provide: https://github.com/tommai78101
I don't know, can you? That is a question only the school can answer with any value. If they want to see your work and github allows you to show that, than it might be so that it's alright. Perhaps they're expecting something more visual, like a video that shows how stuff is working. Contact the school if you want to be sure.
I wanted to know what else I can do to provide an URL. While I was applying to Github for Student plan, it mentioned that I can use Github as a portfolio. I don't know what that means.
You can make a website that shows stuff (screenshots, videos, descriptions, etc) and provide a link to github if they want to see the full source. When Github mentions you can use it as a portfolio, they mean you can use it for just like that, showing your work. You can specify enough stuff on a per project basis to solely rely on it I guess.
I'm sure there are things I'm missing out on, perhaps one can help me criticize about my "portfolio"? Does a Github account work as a "portfolio" as it intended to be?
I quickly went over the github page, There are a couple of projects that go in to a good amount of details, where others just have one line that doesn't really say that much, Just make sure people don't have to go through your code to figure out what something is doing.
Showcase your stuff, screenshots and videos etc.
I personally like a "stand alone" portfolio more to give everything a more personal touch and perhaps some people do not understand the concept of github and never get to see the potential you have.
I'm sure others have more input of value for you. Hope it helps!