Steps to complete this task:
1) Read https://www.mediawiki.org/wiki/Help:TemplateData and https://en.wikipedia.org/wiki/Wikipedia:TemplateData/Tutorial
2) Use the information (especially in the section https://www.mediawiki.org/wiki/Help:TemplateData#TemplateData_editor ) to use the built-in TemplateData editor to add TemplateData to the documentation sub-page of five templates on Wikipedia (any language edition).
At the English Wikipedia, you can find lists of templates that may need TemplateData added in this list: https://en.wikipedia.org/wiki/Wikipedia:TemplateData#Commonly_used_templates There are similar lists at a few other Wikipedias, or you can look for templates manually, in the Template: namespace. Some templates already have complete TemplateData; please remove those from these lists.
Note: It is faster to add TemplateData to templates that have fewer parameters, so you may want to choose simple templates for this task.
3) Post the URLs for the templates you edited. Ask your mentor to check your work to make sure that the TemplateData was done correctly.
4) Think about what you just did, and compare it to the directions you read. Are the directions complete? Are they correct? Were they easy to understand? Try to add missing information and correct errors by editing the pages. Use short, simple, direct sentences. See https://en.wikipedia.org/wiki/Wikipedia:Screenshots_of_Wikipedia for information on how to upload new screenshots. Use a copy of https://www.mediawiki.org/wiki/Help:Sample_page if you need to make screenshots that show non-template content.
5) Contact your mentor to have your corrections and additions to the documentation reviewed. If there is something that you don't know how to fix, then leave a note on the talk page with a description of the problem.
Hours (integer) to complete the task: 5 hours
Beginner task? Probably not (it's a less-technical task, but it will probably take too long for a beginner)