what do i do if i didn’t download the macintosh hd thing after i restated it? my mac has a folder and a question mark in it now.

Hello, i decided that i was going to give my mac to my family member so i erased the info on it.(Restarted) After this it said that i needed to download the new macintosh hd , but when i was about to download it my internet server crashed. This meant that i has to turn off my computer and figure out how to fix my internet. Thankfully, i fixed my internet but what i didn’t know was that after i would try to turn on my mac it didn’t show anything but a black screen with a folder and a question mark. How do i fix this? Help?!