First decide what device you want, X3, livewire, touch screen.....(I'd suggest X3)
Next, buy the device, I'd suggest buying the device from one of the companies that also writes custom tunes (Innovative, Gearhead........) This way you get the device + a few custom tunes for one neat price.
The vendor will mail you your SCT device, download the appropriate firmware and updater from SCT's website, follow directions to load current firmware on the device.
Use device to get your trucks strategy, e-mail this to the vendor you bought from, along with list of mods and what tunes you want, and they will e-mail you back with your custom tunes. Save these, load them onto the SCT device and then onto your truck,