How Do You Put Together A Portfolio?

[allmostanyone]

I understand it's a collection of your best work but up till now I didn't think I had any good work but maybe I do...
I'm applying for the Visualization college here and they ask for a portfolio. I've made many videos as only a hobby, for fun, but my sister's friend who graduated from there said I have some work worth showing, I would have never thought!
So in general, what goes in a portfolio?  

[Clasela]

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I'm taking a wild guess here, but if it's anything like putting together writing samples, then this may be helpful.
From what I've been told, you put in your best work that showcases your specific styles and techniques you use.
Also, have you tried consulting Google? Or maybe even asking someone at the college to elaborate for you?
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[allmostanyone]

Yeah, I emailed the head of the department, i was told to talk to him. I also asked the friend mentioned above but she hasnt been much help with it -_-