Note: if you have not done so, please read the introduction to Upgrading a PS3 Hard Drive before performing these steps.
Once you have reconnected all of the cables, such as power, video, HDMI (everything you normally use when you play on your PS3) you can turn the power on.
The PS3 will recognize that the hard drive you just installed will need to be formatted, and will prompt you, with confirmation, to do so. Say yes to these questions to format the new PS3 hard drive. Once the format has been completed you are ready to use the PS3 with your newer, bigger, and better hard drive. Move on to the next step.