help help help

Hi,
I have a problem....
I need help about Generalized Estimating Equation. The response variable is "efficacy" (numeric) and the predictors are "eziology" (categoric) and "terapy" (string).
After downloaded the gee from CRAN I tried to use this procedure for example:

summary(gee(efficacy~eziology+terapy, id=?, data=pippo, corstr="exchangeable"))

Could you send me an example of application of GEE with two variables?
Thank you very much

Paola Di Stefano