Capisce (pronounced cah-PEESH) is an Italian word that is used in American slang to say "got it" or "understand." The correct word in Italian would be capisci (pronounced cah-PEE-shee) to address the second person informally, a.k.a. you. Capisce, in Italian, is used only to address the second person formally (like when speaking to an elder or someone you don't know) or to express that a third person (he, she, it) understands. The correct Italian pronunciation of capisce is cah-PEE-shay.
To say I understand is capisco (cah-PEE-sko).
You better get outta my house before I break your face, capisce? Yeah, capisco.