Assumption is that you know what LoRa technology. Howevever, if you are not familiar with it basics are:
Topology used by LoRaWan network is laid out in star-of-stars topology. End-devices communicate with gateways that relay messages to network servers. Gateways use sophisticated digital baseband chip (SX1301) that use DSP to simultaneously decode up to 8 frequencies at any data rate. There is a lot more to it than just SX1301 (two more chips are required SX1257 and quite some more circuitry to tune front end RF circuits to 433MHz, 868MHz, 915 MHz or any other frequency band). Best place to get more info is LoRa Aliance.
Read more: Build Low Cost Development LoRa Gateway (Raspberry PI + Multitech MTAC)