How to make a phase shifter?

I've gotten interested in beam-forming via a phased antenna array. I read a few articles/tutorials and they have very nice diagrams of antenna arrays and how the antennas interact to behind each antenna is the key piece: A phase shifter. And yet when searching for it it seems like more of a theoretical device rather than a physical one-yet really phased antenna arrays exist. What is it exactly? Is it something so simple it's just assumed I know what it is?

What, physically, is a phase shifter?

• The parts needed to shift phase depend on the base frequency. – Ignacio Vazquez-Abrams Oct 29 '15 at 7:13
• Different lengths of coax work nicely as delay lines and, of course, a delay line can also be regarded as a phase shifter. So, pick the length of cable you need to produce a delay that corresponds to the correct phase shift at the frequency in question. – Andy aka Oct 29 '15 at 8:17