Naquadah is the basis for all Goa'uld technology.
The Ancients made the first practical application of the mineral with the creation of their network of interplanetary Stargates. The Goa'uld eventually discovered the mineral's potential and absorbed it into their technology. It is a staple of many of their devices and a cornerstone of their powerbase. Worlds rich with naquadah - such as Abydos - are therefore highly prized.
Naquadah is used to power all Goa'uld devices, providing an efficient source of energy. Jaffa staff and other weapons, Goa'uld motherships and other space vessels, communications and sarcophagi are all powered by naquadah. It is even found in the bloodstream of the Goa'uld, though it is not known how it came to be part of the symbiote genetic make-up. In excavations conducted by Dr. Daniel Jackson and Dr. Robert Rothman on P3X-888, the homeworld on which the primordial Goa'uld evolved, symbiotes survive to the present day and none have naquadah in their blood.
Those taken as hosts by Goa'uld symbiotes absorb some of the naquadah into their bloodstream. The presence of naquadah in the blood is the key which unlocks the most vital Goa'uld technology, including the controls of a mothership, and both the ribbon and healing devices. The energy contained within the mineral is tremendous: portable naquadah reactors can power cities (3.05 "Learning Curve" and 4.09 "Scorched Earth") and also construct explosives of terrible destructive power (4.09 "Scorched Earth" and 4.15 "Chain Reaction"). Allied with the host body's bio-electrical impulses, the energy contained within the naquadah in the bloodstream of host and symbiote renders these Goa'uld devices operable when touched (2.01 "The Serpent's Lair" and 2.06 "Thor's Chariot").
Goa'uld can detect the presence of naquadah within a host body. Seth (3.02 "Seth") and Hathor (3.01 "Into The Fire") both detected that Samantha Carter had been taken as a host. It can also be sensed within the Stargate itself. Hathor was drawn to the Stargate even though it was buried beneath Cheyenne Mountain (1.14 "Hathor").
Those taken as hosts by Goa'uld symbiotes absorb some of the naquadah into their bloodstream and even if freed from the parasite, retain the ability to sense that presence in others. This was first demonstrated by the orphaned Cassandra Fraiser, who sensed the Tok'ra symbiote Jolinar of Malkshur within Samantha Carter (1.02 "In The Line Of Duty") some time after a naquadah bomb constructed within her body by the System Lord Nirrti decayed and was absorbed into her bloodstream. Carter too has sensed the presense of naquadah within other beings. (5.08 "The Tomb")
Thus, the Goa'uld dependency on naquadah has become an inextricable part of their physiology and genetic makeup.