Question mark folder

Hello, so I wanted to reset my mac so I erased it all at the login window to start again and now all that comes up is a flashing folder with a question mark on it with ‘support.apple.come/Mac/startup’. Once there, it said the following:

“A folder with a flashing question mark means that your startup disk is no longer available or doesn't contain a working Mac operating system”

how do I fix this issue?