First off, thank you for considering contributing to Zotero Notification. It's people like you that make Zotero Notification such a great tool.
If you've noticed a bug or have a feature request, make one! It's generally best if you get confirmation of your bug or approval for your feature request this way before starting to code.
If this is something you think you can fix, then fork and create a branch with a descriptive name.
A good branch name would be (where issue #325 is the ticket you're working on):
git checkout -b 325-add-pdf-export-feature
Make sure you're testing the changes you're making. Refer to the README.md for instructions on how to run the project. For testing locally, you can use XAMPP or WAMP server.
Work on the code to fix the issue or add the feature.
At this point, you should switch back to your master branch and make sure it's up to date with Zotero Notification's master branch:
git remote add upstream [email protected]:aritraroy24/zotero-notification.git
git checkout master
git pull upstream master
Then update your feature branch from your local copy of master, and push it!
git checkout 325-add-pdf-export-feature
git rebase master
git push --set-upstream origin 325-add-pdf-export-feature
Finally, go to GitHub and make a Pull Request :D