Here are steps to do so:
- Create an account on Wikipedia
- Search for an article on Wikipedia about your favorite topic
- Read the article and make small edits to it. Edits could be fixing spelling mistakes, typos, adding images, new content, etc
- Tip: Before you add new content, make sure you understand five pillars of Wikipedia https://en.wikipedia.org/wiki/Wikipedia:Five_pillars
- Once you are done editing, save your changes
- On the Google Code-in website, add a comment on the task, mention which article you edited, new changes made and a diff link (see how to create one https://en.wikipedia.org/wiki/Wikipedia:Complete_diff_and_link_guide#How_to_create_a_diff_link)