How to install a 2nd monitor to your mac

Buy a Mac

Connect one end of DVI cable to the Adapter

Connect other end to monitor

Plug in the adapter to your Mac's mini display port

Open System Preferences

Choose "Displays"

In the "arrangement" tab, align the 2nd blue box (the one without the white horizontal bar on top) to how your 2nd monitor is positioned

See how it's aligned even if my monitors ...

... Are on different levels