Steps:
Go to google.com type in power bi desktop

Click the link to the Microsoft Page of Power BI Desktop

Next go to the page and click the download button

On the next page click on the check box PBIDesktopSetup_x64.exe and click the next button

Download will start automatically as soon as u click

After that double click on the PBIDesktopSetup_x64.exe file and your file will be installed.
Click on the desktop file and your Power BI Desktop will be on the output window.
This is the Power BI window: