Once it finishes downloading, the installer will open automatically and you will be prompted to begin. The first part of the installation process just involves agreeing to Apple’s term and conditions. If you decide later that you want to read (or re-read) all of the terms and conditions, you can find them on Apple’s website.
You’ll need to confirm once again that you read the terms and conditions.
Having recently went through the process of updating a handful of Macs to the latest versions of OS X as part of a gifting tech support campaign, several Macs developed an odd flickering display problem that was only visible when an external monitor was connected to the Mac.
Just click the Time Machine icon to see when when your last backup was completed. When you plug in any external hard drive for the first time, a pop-up will appear asking if you would like to use it for Time Machine.
It will tell you what type of Mac you have, the screen size, the year it was purchased, and whether you are currently covered under Apple Care.
If your machine is supported by Mavericks, it is recommended that you have a backup of your data before updating.
Others have taken to Apple's own forums to seek support and assistance.
We've put in questions to Apple, but did not hear back at the time of publication.