Yo Kass answered
The verb 'to understand' in Italian is capire, and whilst, in English, the verb 'to understand' breaks down very easily into: I understand, you understand, he understands etc... Italian conjugations are a little bit more varied and make it a trickier to translate the word 'understand' without context.
The following is the conjugation of the verb capire in the present indicative form which is a tense you will hear in use fairly often:
Io (I) - capisco
tu (you) - capisci
lui/lei (he/she) - capisce
noi (we) - capiamo
voi (you pl.) - capite
loro (they) - capiscono
Outside Italy, one popular context in which you might hear the verb capire being used (amongst other Italian vocabulary) is in the 'Mob' or 'Mafia' genre of movies and TV programs like The Godfather, The Sopranos, or Goodfellas.
For example, if a mob boss were to receive a phone call regarding the location of a cache of weapons, he might use the word capisco to show that he understands the information being relayed to him.
In contrast, if a mob boss wants to warn a rival against making a rash decision he might say something like 'Don't try anything funny,' followed by 'capisci?' meaning '(do you) undertsand?'