IMPORTANT: Keep in mind a Clean Install means erasing (formatting) your Macs internal drive so ALL data will be wiped.
Is that your intention?
If you need to save data from your current internal drive then let me know before proceeding for additional information.
I would recommend downloading El Capitan via App Store (the full installer will be "Install OS X El Capitan" (6.08 Gb) in the Applications folder), quit it as soon as it auto launches (you will be able to Quit it after you select a language and select Continue), use an 8 Gb USB flash thumb drive to create a USB installer drive:
http://arstechnica.com/apple/2015/0...able-os-x-10-11-el-capitan-usb-install-drive/
Recommend you try the latest Diskmaker X 5.0.1 first (if you have a problem with that we can try the Terminal):
http://diskmakerx.com
Here is some more information of what we are trying to accomplish with the USB Installer (the article discusses Mevericks, but it is still good information):
http://www.hongkiat.com/blog/clean-install-mavericks/
After you create the USB installer,
TEST it.
1. Plug it in to the computer
2. Restart holding the option key
3. Select to start up from the USB installer, be patient it takes awhile to start up because USB thumb drive is slower.
4. After it starts, select a language.
If you are not ready to install then at this time:
5. After you get to a window showing things like Time Machine, Install OS, Disk Utility etc., STOP. Go to the upper left
menu and select Restart. That is a successful test.
6. Let the Mac restart normally and get to the normal desktop. Eject the USB thumb drive, remove it and save it for later.
IMPORTANT: We will use the USB installer to format (erase) the new drive for Mac Extended (Journaled) and install the El Capitan OS.
When you are ready to install OS X El Capitan:
1. Make sure the MacBook Pro (MBP) is connected to a power source first.
2. Plug in the USB installer thumb drive.
3. Power on the MBP with the option key held down.
4. Select to start up from the USB installer, be patient it takes awhile to start up because USB thumb drive is slower.
5. After the USB installer starts, select a language.
6. Format your drive (
ALL DATA ON THE INTERNAL DRIVE WILL BE ERASED):
. You should see a OS X Utilities screen showing a list:
. Restore from Time Machine Backup
. Install OS X
. Get Help Online
. Disk Utility
.. A) Select Disk Utility
.. B) Once Disk Utility is open, select the internal drive from the list on the left. Once you have the disk selected, click on "Erase". Set the Volume Format to "Mac OS Extended (Journaled)". Name the the Volume "Macintosh HD". Once you've formatted your drive, you can close Disk Utility.
7. Install OS X on your internal drive:
Select "Install OS X" on the OS X Utilities screen.
Follow the steps as they are presented to you, making sure to select your new drive (the one you just formatted in the previous step) as the install location. The installers for Mac OS X are very straightforward to use; all you need to do is follow the on-screen instructions. Once you have filled in the required information, the actual install will begin. This can take quite a while. BE PATIENT.
Note: During the installation process, you may experience the indicator hanging at “About a second remaining” (or some other period of time) for many minutes. Do NOT cancel, just wait it out.
Your Mac will then restart, and will wrap up the installation process in another 30 – 40 minutes. When this is done, your Mac will restart automatically (again), leaving you at the login screen of a fresh copy of Mac OS X.