To make the copy, you just have to install the DiskMaker X application on your computer, download a copy of Yosemite, and follow the assistant's steps to set it up. You must have a USB drive with at least 8 gigabytes of space and free of important files since the memory will have to be completely reformatted to make a copy of the operating system.
If all goes well, after a few minutes, you'll have a Yosemite installer on the USB drive that you can then use to install a clean copy of the operating system on your Mac. Its own developers describe it as the easiest way to create a boot disk for OS X.
What's more, this tool is not only useful for Yosemite but also supports the Mavericks and Mountain Lion installers as well.
NotesMac OS X 10.6x or higher is required to run this application.