If you are a new freelancer with no portfolio to back you up, don't worry. I didn't have a portfolio either. But you can get one fast and simple!
Write your own examples to showcase. If you write cover letters or resumes, write fake ones that you can add to your portfolio.
Ask your friends or family if they need something written for them and use those to showcase in your portfolio.
This worked for me, and as I began getting clients, I started building my portfolio from the projects I completed with them.