Controlling 12v components with a 5v microcontroller

Total newb, sorry if I'm in the wrong place. I want to create a circuit that will allow me to control 2 cameras. They both require 12v power. I want to have a microcontroller (i'm using an atwell ATmega328 with the Arduino bootloader) control power to each camera, as well as switch the video input between the two of them. I also need to use a 12v power source as an input to the microcontroller. I think I need to use relays to control the power to the cameras. I was planning on using these SPDT relays. I'm not sure if I can connect these directly or if I have to use transistors. I'm also not sure how to switch between the video inputs. Should I use relays for those as well? And can I simply use a voltage regulator to bring the 12v input down to 5v?

I apologize for how confused I am, but I'd really appreciate any advice you all can offer.