Before you start up your new computer, it is important that you read the manual that came with your motherboard about first time use.
One of the first steps you will have to do is format your hard drive. A lot of hard drives that are newly purchased offer software for you to stick in your disk drive that will automatically boot your computer to set up your hard drive. Please consult the manual that came with your hard drive.
You will have to install some kind of operating system for your computer. Depending on what you use your computer for will decide what software you choose. The most popular operating system thus far is Microsoft Windows. However, Linux is gaining popularity rapidly.