Well, your computer just finished to download the latest image of Raspbian (it should be Buster currently) and now you want to install it on your fresh new SD Card. So how to do it?
If you are looking for install Raspbian on SD Card the first step is download BalenaEtcher, no matter what OS are you using: it works on Windows, Mac OS and Linux!
Install it of course and that’s it.
In the following image you can see how easy the whole process is: select the image that you want to install on the SD Card, Select the Drive (insert the sd card or the card reader) and than click on flash. It will ask for the password (of your computer), so insert it and the process will start.
Enjoy your raspberry pi with your fresh new OS.