Why retina mac book pro won't output signal to second monitor via mini display, but detect it? I have 2 monitors, a retina, 15-inch, mid 2014 mac book pro.
I plugged the hdmit output to one monitor, and a mini-display to dvi to the second monitor.

On mac book preference system perferences->displays-> arrangement tab I can see all three screens, however the one connected via mini display port - dvi isn't getting any signal. 

Can I used two monitors with a mac book pro, without having to buy some fancy extra device?
Your model should support 2 external monitors at max resolution of 2560x1600.

Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 2560 by 1600 pixels on up to two external displays, both at millions of colors.

Check your resolution settings, if the cables are working.

https://support.apple.com/kb/SP704?locale=en_US