Depending on your field, having a portfolio may be critical to showing potential employers your creativity and the thoughts behind your creative work. It helps showcase your approach towards solving a particular problem, and part of the content would also be your designs, depending on the nature of your portfolio.
If you are a User Experience Researcher, it is vital that you create a portfolio that showcases the research problem, objectives, methods, and how you handled the entire research process from start to finish. The more content you have in your portfolio, the more potential employers can gain more insight into your ability. If you are a graphic designer, tell your story in the most granular manner, allowing them to see your designs, the concepts and approaches.
Beyond helping you to get a full time job, your portfolio also exposes you to getting part time jobs and gigs which you can do as a freelancer, thereby giving you the opportunity to increase your income.
A good place to create your portfolio for the purpose of getting a job is Behance, depending on your kind of work. For freelancers, Fiverr and Upwork are amazing platforms to build your portfolio in the world of freelancing.