Hi there jesuislepop,
A website called something like partsguru (google it) lists a number of parts diagrams including Saecos. The files are downloable - pdf from memory. The last time I looked some machine models had numerous model changes as the manufacturer changed designs so you might need to start with the newest and work back in time.
The starbucks version might be a little different too.
A cam is an eccentric or off-round wheel. A non-circular circle. It will be mounted on a shaft or spindle. As it rotates (maybe as a knob turns the spindle) the distance from cam centre* to outside edge changes relative to a fixed point. This then might flip a microswitch that operates a pump or valve. Depending on the quality of the diagram it might appear circular but you should be able to recognize the location from the diagram.
Anyway the Via Venezia parts list will possibly be in Italian.
Cam in Italian is cammo - oops should be camma[/edit] or eccentrico (thats what Fiat calls them).