After install, click to the library tab in the left side of launcher. Or just use the orange “Launch” tab in the top left corner. Wait a few seconds. Then it will open the project window. Select the directory of your project, then type in a name of your project and press “Create Project”. And again wait a few seconds. And it’s ready. Now you are in the Unreal editor.
https://docs.unrealengine.com/latest/images/Engine/Basics/Projects/Browser/NewProject_FPSExample.jpg