ZigBee Modules are small integrated boards which are tested, calibrated and pre-certified so you can add ZigBee functionality without these complications. Module manufacturers are generally helpful and can help you with embedding ZigBee into a design and overcoming technical hurdles.
ZigBee is a wireless networking standard built on the IEEE 802.15.4 standard which defines the physical and MAC layers. It is best suited to low bandwidth applications and has a range of up to 70 metres but data can be sent further if relayed through a network of ZigBee nodes.
A possible alternative to a ZigBee Module is a System-on-Chip (SoC) with integrated ZigBee.