I'd recommend starting with the Atlassian University. Now a number of their courses are frozen while they do some behind the scenes work, but I think their free sessions are still available.
Also, I'd recommend heading over to the New to Jira group, I'm sure there are some questions that have been asked there that might help, and if not feel free to ask, people will be happy to help you there.
Definitely take advantage of the resources Jimmy provided, but in addition you can also take advantage of the Atlassian YouTube channel: https://www.youtube.com/c/Atlassian/featured. There are tons of video's there about Jira including introductions to Jira and lots of others to help you get familiar with Jira software. Just another tip; Jira and Confluence work great together. Atlassian has a whole channel now dedicated to Confluence so be sure to take advantage of that as well!
