How to set up dual monitor on a Mac? I have an iMac Retina 5k 27", late 2015 and I also have Dell monitor which supports VGA, HDMI,and  DVI inputs. I want a dual monitor setup by using this Dell monitor as the second monitor.

My question is how can i do it? Should I use a cable converter to connect it? Is there setting should I change in macOS? 

I  bought a DVI to Thunderbolt converter. When I tried to plug it in, I just saw a blank screen in second monitor.

Here is the specs of iMac:


iMac (Retina 5K, 27-inch, Late 2015)
Processo: r 3.2 GHz Interl Core i5
Memory: 8 GB 1867 MHz DDR3
Startup: Disk Macintosh HD
Graphics: AMD Radeon R9 M380 2048 MB
You will find in System Preferences a control panel where you can set and control where menus appear etc.

Also, you can set the mirroring options to appear in the menu bar as necessary.

Personally, I would purchase adaptors to go for the HDMI input to the second monitor.