device and sub-circuit models

I am facing difficulties in including device/sub-circuit models into gnucap
simulation.
Specifically for transistors & analog ICs such as opamps.
It appears to me that application package does not have any and we have to
create. Am I right?
Is it possible to use available spice models? If so how to make them
compatible with gnucap.
how to ensure pin compatibility of imported model & my circuit.

Apologies for very basic questions (I have not used Spice earlier )

-- 
vsrk sarma