A Portfolio is a collection of things, such as investments, photographs, drawings or articles. A freelancer, no matter in what professional fields, should have a portfolio to showcase the projects done and keep update it through time.

Where to put your portfolio?

There are so many ways to keep track of your portfolio.

CertificationPoint of course...was built for student portfolios
Google Drive or Google Doc. Open a folder with public access, and drag in all the portfolio files. You can use a word file for each job you’ve done, describe the company, the time it takes, the scope of work and achievement, and the budget. And of course add your contact details.
Drop box. It works like Google drive, and it’s very good for graphic designers to showcase graphics and videos.
Your own website or blog. Use blogger, google site, medium, Quora blog (like this one), free wordpress blog or any other blogging service you like as a place to demonstrate your works. This is essential for freelancers related to writing, you must first show your writings.

Such portfolio can save you lots of time and energy, whenever you approach a customer you just have to drop the link and invite them to see what you have done.