how to learn jira
Very simple answer - use it. By far the best way to learn things like this is plain experience. There are courses and books available, but they can't teach you as widely or as fast as just using it.
Find a project that needs some form of tracking, install and configure JIRA to help you do it, then use it to track the project.
See https://en.wikipedia.org/wiki/Homo_Ludens
and then play with a local instance of it. Get yourself confused, clear up the confusion. Repeat
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