Display Your Work
In my opinion, building a web development portfolio is the most exciting thing a web developer could do. It is a mixed bag of work displaying your skills, and professional projects that you take pride in. But before you get to the point of having any professional work, it can be a long road of trial and error, and will help you decide if this is the career that you actually want.
You Have to Start Somewhere
Your first portfolio piece is without a doubt going to be your least favorite. It's going to take longer than you thought it would, and will make you hate the craft.
Well, what should it be? In all honesty, your best bet is to take a website that you frequently visit and do your best to recreate it. This is going to put your development skills to the test, and will help with practicing how to convert designs in to fully functional websites. I recommend doing this at least a handful of times and choosing your favorite to display.
After this, move along to making more apps, they can be calculators or fun little things like a coin flipper or a to-do list.
You have now found a way to display your skills in the big three web development languages. So what now?
Now, you can move on to some real world projects, ask around your town and look for any potential clients. Don't be afraid to do your first one for free.
Maybe the coffee shop down the street needs an online presence, or the pizza place around the corner needs an update. Now is your time to shine and don't give up until you secure a client and show them that you mean business.