Portals are the main source of transportation in the Towers. They have been around as long as the spires themselves. It's speculated that the art was created the same time the Seal was put in place. However, modern study has been shifting the older methods into more stable applications that have a better Harmony with current philosophies. This arcana in particular is the methodology that Ziedas Laukyme has tweaked.
Casting is done by intricate hand movements that weave the space between two places together. Some say it is similar to knitting or conducting music. As a player reference, it looks very similar to the finger tutting that was used in Doctor Strange, The Magicians... and Naruto. It can be anywhere as simple as typing on an invisible touchscreen to an hour long routine.
The philosophy of space is that it is as infinite as it is terrifying. One needs a massive amount of courage and determination to open a way. If you think about it, a portal is essentially transporting all of your atoms from one spot to another. Misstep, and you could be thrown into the Void. Maybe. Those unlucky few who broke their concentration never really got to tell how horrible of an end it was, seeing how no one has really come _back_ from a bad Doorway.
Technicians that run maintenance on the main gateways do not need as intensive training as those who create their own Doors. There are many schools of thought in the realm of Gates; being trained by a renouned Gateway Magus is a lot like getting into an Ivy league college, while techs are more or less thought of like trade schools.