Erased Hard Drive and operating system accidentally via disk utility? Here's what to do

Question

I thought I had messed up majorly today when I attempted to erase and re-install an operating system on my friends macbook pro. I used another computer and targeted his computer so his hard drive would show up on my desktop. I then used disk utility and completely erased his hard drive. "Ooops" i thought after trying to then install Lion from my computer's applications folder. Wouldn't work. All his computer would show was a folder with a ? mark!!!
I searched for a solution as to what to do in this situation and got a lot of conflicting complex suggestions. The one that made the most sense was to create a bootable external disk to reinstall the system. This didn't work for me, I was probably doing it wrong.
HERE'S WHAT DID WORK FOR ME:
(what you need)
1) decent wireless internet connection (know the network and password)
2) blank computer hard drive (no OS, no nothing)
3) power cable
thats it
Step 1.
Restart your computer and hold down "Command" and the "R" keys at the same time. do this for about 30 seconds or so and release
Step 2.
Your computer should, after a few seconds or so, show a spinning globe. Your computer will then start searching for an internet connection. Choose a network from the drop down menu and type in the password to the network.
Step 3.
Your computer will then connect with Apple.com's software site (I think this is called OSX Recovery or something [thus the holding down of the "R" for recovery key]) and find your computer's original operating system (not sure how far back this works, but it worked perfectly with Lion)
Step 4.
Download the OS
Step 5.
Upon download completion your computer may shut down. Just turn it back on and when its back up and running it will immediately start to install the OS it just downloaded.
Step 6.
Wait for this to complete and bam, you're back to having an operating system on your computer.
I hope this works for anyone with my problem.
Good luck!

Answer 1

You will need to do the following:
Install Mavericks, Lion/Mountain Lion Using Internet Recovery
Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.
Boot to the Internet Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND-OPTION- R keys until a globe appears on the screen. Wait patiently - 15-20 minutes - until the Recovery main menu appears.
Partition and Format the hard drive:
1. Select Disk Utility from the main menu and click on the Continue button.
2. After DU loads select your newly installed hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.
3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the process has completed. Quit DU and return to the main menu.
Reinstall Lion/Mountain Lion. Mavericks: Select Reinstall Lion/Mountain Lion, Mavericks and click on the Install button. Be sure to select the correct drive to use if you have more than one.
Note: You will need an active Internet connection. I suggest using Ethernet
            if possible because it is three times faster than wireless.
This should restore the version of OS X originally pre-installed on the computer.