The best thing that you can do is study examples of portfolios from people who just got a junior developer job.
Look at what kinds of projects they had.
Look at the layout.
Research is your best friend 
There are tons of examples to look at.
You can start with the forum.
Here are a couple to get you started.
Search on twitter, linkedin, github.
If they list themselves as a junior dev, take a look at their body of work.
Also, there are plenty of youtube videos and articles that talk about how to build a portfolio.
Good news is that there is tons of information to help you.
You just have to look for it.