There a numerous GUI program’s out there to create a stick but’s it super duper easy to do it from the terminal as the App store image contains a shell script that does it for you with just one Terminal command. So go ahead download a fresh copy of Mac OS High Sierra via the app store, connect a 8Gb or more USB stick and fire up your terminal.

$ sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia \
--volume /Volumes/Yourstickname --applicationpath \
/Applications/Install\ macOS\ High\ Sierra.app/

Of course you have to substitute the “Yourstickname” with the name of your stick. You can find’s it name by typing `mount` in a terminal.