Everyone can help an open source project: you don’t have to be a programmer or a terminal guru. There are other stuff besides code in open source projects: documentation, for example. And there are a lot of projects without code at all: books and some others.
But not everybody knows that it’s possible using only a browser.
Find a file you want to edit on GitHub (you need to be logged in) and press Edit button:
Edit and save a file:
Just after saving you’ll be prompted to send a pull request:
Describe your changes and press Send pull request button.
That’s all, you’ve made the world a bit better.