Yes, there are bugs in Liferay! Fixing one is a great way to learn your way around the project and contribute back to open source. You'll find a list of recent bugs that have been marked as easier than most, so if you want to give it a go, pick one, and follow these steps to fix it!
Fork the Liferay project on Github. You'll need a Github account, and then visit the Liferay Portal project and click the Fork button.
Follow the steps to setup your development environment, using your preferred developer tool.
Build and start Liferay, and see if you can reproduce the bug. This is super-important, because if you can't reproduce it, you won't know if you've fixed it!
Learn the basic code structure of Liferay, and see if you can find the place where the bug might be. Take time to learn the area of the code. If you need help, contact the module lead for the area of the code.
Try to fix the bug, rebuild and restart Liferay, and see if you've fixed it! If not, keep iterating until you've fixed it. Try not to touch more code than is absolutely necessary.
Commit the code change to your git repository, and issue a pull request to the right person. Check out the components list on issues liferay.com, and find the module lead for the area of the code in which you've made changes. This is the person to which you should send the pull request to, so you'll need to find their github account name (chances are it's one of the top 20 contributors). Once you're confident of your fix and know who to send your pull request to, send it and congratulate yourself!
Click Contribute Solution on the bug report on issues.liferay.com to document that you fixed it and have recorded the pull request, and congratulate yourself on giving back to our community!