How can I recognize clearly when I deal with capacitors in parallel or capacitors in series? Can follow a "rule" or a intuitive method? I have to do difficult exercises regarding system of capacitors so I must understand when I have capacitors in parallel or in series. Can you explain me in a simple way?
In the absence of supporting information, it's hard to say where to start. Do you have a circuit diagram, at least?
Typically one would identify certain nodes at which the voltage(s) are known, then trace all electrical paths to figure out which capacitors have that node in common (suggesting parallelism), and which capacitors are connected in sequence on the way to another voltage node or ground point.
For a simple example, if caps A and B are tied to +V, cap A's other plate is tied to ground, cap B's other side is tied to cap C, and the far side of cap C is tied to ground, then:
1) B and C are in series, so calculate the equivalent capacity(B-series-C). 2) that equivalent capacitor is in parallel with A, so calculate the equivalent capacity (B-series-C) plus A .
In general, start with the smallest groupings and work your way up to the top-level this way.