I think the SHOCKS option is documented fairly clearly in the "FORECAST" section of the Reference Manual.
Briefly, you can either define the vector of shocks ahead of time, or provide the vector using the literal matrix notation. For example, if you had a 3 equation model, the option would be something like
shocks=||s1, s2, s3||
replacing s1, s2, and s3 with the desired shock for each equation.
