As tempting as it may be to get on with the installation, I recommend quitting the installer at this point and taking care of some setup details first.El Capitan was announced at WWDC 2015 and will go through a public beta process beginning in July 2015, finishing with a public release on September 30, 2015.
OS X El Capitan can be found in the Mac App Store as a free upgrade for anyone who is running OS X Snow Leopard or later.
Should you have a Mac that meets the minimum system requirements for El Capitan, but is running a system earlier than OS X Snow Leopard, you will first need to purchase OS X Snow Leopard (available from the Apple store), and then follow these instructions to install Snow Leopard on your Mac.
Don’t take any chances with your data, when a simple backup offers a great deal of insurance.
Gone are the days of complex install options, such as Archive and Install, which backed up your current system and then performed an upgrade install.
Before you decide to participate in the public beta or install the new Mac operating system once it's released, you should take a look at which Macs will support the OS, and what the minimum specifications are.
You can find out if your Mac is up to snuff by taking a look at this guide: OS X El Capitan Minimum Requirements Once you have determined that your Mac meets the requirements, you’re almost ready to proceed with installing the new system.Clean Install derives its name from the first step of the process: cleaning the target volume of any system or user data.This is usually done by first erasing the target volume and then installing OS X El Capitan.Let's move on to Page 3 and start the actual installation.At this point, you've backed up your data, checked that your Mac meets the requirements for running El Capitan, downloaded the OS X El Capitan installer from the Mac App Store, and created a bootable copy of the OS X El Capitan installer on a USB flash drive.When your Mac first starts up after a clean install, the initial setup wizard will walk you through the process of creating a new administrator account. The clean install option is a very effective way of starting over and may be a good method of installing a new OS if you've been having problems with your Mac that you just can’t figure out.