The Windows startup folder is essentially a folder which you can place programs (or shortcuts to programs) or scripts that you want to run/open when your window starts. Hence the startup in the name.

To find out your Windows 10 startup folder. You have two options. Use your run command copy paste or type: shell:startup (right click on your start/window icon to bring up the menu).

This should bring you to the folder directly.

C:\Users\Username\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup

If you wish to find your startup folder for all users on the system, you’ll need to instead run shell:common startup, which would bring you to:

C:\ProgramData\Microsoft\Windows\Start Menu\Programs\StartUp