Confused on how to reinstall OS and erase the drive - iMac

[kaplaninternational]

Guys I am having a weird problem - I am selling my iMac and I went to System Restore screen and I unmounted the main drive and erased it.

Now when I go to reinstall OSX it doesn't find a drive

So then I had to connect an external drive and install it on that.

How do I sort this out so I reinstall OS on the actual iMac drive so I can pack this and sell it?

 

[kaplaninternational]

When I go to my disk utility:

It shows me:

APPLE HDD ST....
1TB SATA Internal Disk
Unformatted

Do I erase this? And if so what do I choose when I do that?

-

Then I also have

APPLE APFS MEDIA
It says 1TB Uninitialized

-

Then it's showing a third drive as internal called:

APPLESSD Media
And it says unformatted here

 

[NoBoMac]

Sounds like the recovery partition was erased. Might try to do an internet recovery to get back to square one.

 

[Fishrrman]

What year was the iMac made?

 

[Weaselboy]

https://forums.macrumors.com/posts/22923194/

It looks like you have a Fusion drive setup there that is borked. command-option-r boot to Internet recovery then format both internal drives. Then follow the steps in my post above to put the Fusion drive back together. After that reinstall the OS.

Let me know if you need more specific steps.