What you want to do is create “spec work.” These are projects that reflect real-world briefs but are for an imaginary client. You find (or create) a brief, then strategize, execute, etc. You then create a case study on it and display it on your site. This will help build out your portfolio and illustrate to potential clients/employers you are capable of doing the things you say you can.
Once you get your site nicely filled out with examples of the various types of services you’re providing , you gotta hustle. Cold call, network, call in favors, knock on some doors. You have to be very proactive in finding clients. They won’t come to you in the early days.
One note – it’s often better to focus on a niche, as it will help get you a bit more attention. Let’s say you are focused on baby gear. All of your portfolio is baby related, and you only approach car seat manufacturers or stroller companies. You will have a better chance of getting traction than someone who has a generalist approach and does work for restaurants or autobody shops. Good luck!