Ahh..
Well they are pretty simple to set up and use. I would concentrate on setting up the iPhone first and after you have it set up then you can begin setting up the iMac. Simply turn on the phone and it will guide you through the process.
When you get to the point that you have the iPhone working and are ready for the iMac then turn on the iMac and it will guide you through the setup. If you have information you want to migrate from the PC to the Mac then I'd recommend using Migration Assistant which is described in https://support.apple.com/en-us/HT204087 . Do not connect the PC and Mac using Wi-Fi, please use an Ethernet connection as Wi-Fi cannot handle large amounts of data.
Welcome to the light side, you should have fun! If you get stuck anywhere along the way, you can call AppleCare , their phone number in the US is 800-275-2273. If you are outside the US, please use this link: Complimentary AppleCare Support