1. Grab a USB flash drive that's at least 8GB
2. Download Yosemite from the app store (should download to your applications folder)
3. Open disk utility and do the following:
-highlight the USB drive in the left column
-click on the partition tab
-select "1 partition"
-click "options" and select GUID Partition Table
-under name just type: USB (it will be renamed later)
-under format choose "Mac OS Extended (Journaled)"
-click "apply" and "partition"
4. Now open terminal (found under utilities) and paste the following into it:
sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/USB --applicationpath /Applications/Install\ OS\ X\ Yosemite.app --no interaction
-just paste that into terminal and hit enter, it should ask for your password and then the OS will create factory restore media from the USB stick and the Yosemite installer you downloaded from the app store (Note: can take 30-45min depending on speed of flash drive so don't remove the USB drive or exit terminal until it says it's finished)
5. To boot into the installer, just restart the computer and then hold down the "option" key during boot to bring up the boot menu
-select the Yosemite installer from the boot menu (can take quite awhile to load)
-if it's a new SSD, you should be able to simply follow the on screen instructions
-if the USB has another OS installed on it, just open disk utility and erase it
-simply bring your mouse to the top of the screen and the menu bar will appear (disk utility is under "utilities")
The above will install a factory fresh (just like you get with a brand new mac) copy of Yosemite on the SSD.