Check out Video #5 of Power BI Series and learn about DAX Measures and Slicers in Power BI Desktop.
This video covers:
- How to create a Measure
- Intro to Quick Measures and standard calculations
- Intro to Slicers and Edit Interactions
If you are starting learning DAX I suggest:
- Book: Power Pivot and Power BI by Rob Collin & Avi Singh. This was one of the first books I read about DAX.
- Blog: DAX Fridays by Curbal.com . Ruth releases a video every Friday covering DAX functions (and more) and to date, the playlist counts with more than 80 videos. Awesome work .
There are plenty of other sources (books, blogs, videos, etc), but these are my recommendations if you are new to DAX and Power BI and want to learn the basics.