The following steps make your task simple to create a measure using Power BI DAX.
1. First, go to the Power BI Desktop app.
2.Right-click the Sales table or hover over More options (...) of Field pane.
3. Once the menu presents, select New Measure. This activity stores the new Measure in the Sales table. You can also create a new Measure from the Power BI desktop ribbon in the following way.
Go to Home tab > Calculations group > New Measure.
4. Next, the Formula bar exists on top of the reporting canvas, where you can edit your name and write a Data Analysis Xpression formula.