The way these work, is anywhere you have Pylon Power, you can have your units created there...no longer do they just come from your buildings, they can just materialize.
Asking my ally to activate his Sentry's shield. Sentry's are units that have a weak attack, but can create a shield bolstering your Plasma Shields and giving +2 armor.
We're finishing off Red's base here. He has a Planetary Defense Fortress, an upgrade to a Terran Command Center. It's actually pretty powerful, and drove off our initial Zealot rush.
Not being shown in this picture, but another cool ability of the Sentry is to create false barriers. You can trap enemies, make them go around the barrier, or keep enemies out of your base for a while.
The large white squares on the above pic's Mini-Map are Xel'Naga Towers. They don't do much...other than reveal a large portion of the map while you have a unit standing next to it.