Take three open bug reports in Wikimedia Phabricator which have not seen any update for two years. Go to the advanced query form on https://phabricator.wikimedia.org/maniphest/query/advanced/ , search for open tasks only, and set "Updated Before" accordingly (see https://www.mediawiki.org/wiki/Phabricator/Help#Searching_for_items for help). Read those reports that have an interesting summary and try to understand them (if they are technically too complicated or if the English is too advanced you will have to choose other reports instead - this can happen quite often but will help you getting an idea of how complex software can be). If you understand what the report is about, test if you can still reproduce the reported problems (and if the steps to reproduce are clear enough). Add a comment in the bug report and explain clearly which steps you performed and the version that you tested with (e.g. for MediaWiki you can find this information on the page "Special:Version"). Free choice of tickets! Note that some bug reports might be easier to retest (for example on https://test2.wikipedia.org ), some might require special permissions to access certain pages or setting up MediaWiki yourself - up to you if you want to do that. Find out more about updating and handling bug reports on https://www.mediawiki.org/wiki/Bug_management/How_to_triage . Also note the "testme" project - tasks in that project are tasks that somebody wants to see retested (once retested and having added your comment, you should remove that project from the task).

Students are required to read Wikimedia's general GCI instructions at https://www.mediawiki.org/wiki/Google_Code-in_2014#Instructions_for_GCI_students first!