Requirements:
You need to make sure that you've forked and checked out the CoApp website, and you've modified the website content.
Pushing changes to your fork
So, you've modified the website and you've locally committed these modifications to your fork of the CoApp website source code:
c:\project\>cd coapp.org
c:\project\coapp.org\>git commit -m "Updated developers.html with..." src\dynamic\pages\developers.html.md.ejs
It is a good idea to get recent updates from the project upstream:
c:\project\coapp.org\>git fetch upstream
c:\project\coapp.org\>git merge upstream/master
Typically, you want to push all the updates to your fork of the CoApp website project at GitHub:
c:\project\coapp.org\>git push origin master
Now, you have pushed your changes to your fork of the CoApp website repository (upstream).
Submitting your changes to the upstream
As you've learned by the way of forking and checking out the CoApp website, collaborative development of the CoApp project is based on the Fork + Pull Model defined by GitHub.
In order to contribute your modifications to the mainstream, you need to generate and send pull request to the CoApp website team.
Simply, follow the Send pull requests guide at GitHub.