There's a few good ways you can increase your knowledge with Atlassian Tools:
Training: Take some training via Atlassian University. This page is a good starting point; pick the learning paths which most interest you and do some training courses.
Product Guides: Read through the product guides - each product has a Knowledge Base of information about how it works. For example, see the product guide for Jira on this page.
Practice: The best way I find to learn is practice - if you have Atlassian tools at your current place of work, ask if you get involved in administration. Or get your own versions of Jira, Confluence and Jira Service Desk and use the training and product guides to practice using the tools.
I find the Community a great learning tool. Lots of questions have lots of different scenarios - try to find the answer each time and it'll help you learn with real-life examples.
