Gelato is sometimes lableled as "Italian ice cream" in the US, but that definition is probably wrong. Gelato is closer to ice milk, as the Italians have found that too much butterfat interferes with the transfer to the tongue of the fresh flavors Italian gelato is noted for. In fact, it would be illegal in the US to call Italian gelati ice creams, as ice cream is defined by the FDA as a frozen product with no less than 10% butterfat--and typical Italian gelato is lower in butterfat. (Gelati is the plural of gelato.)
A gelateria will often sell fancy gelato concoctions, a simple cone (cono), or a cup (coppa). You pick the flavors, which are labeled, often with pictures. For more, see Where to Find Gelato - How to Order Gelato.
The Gelateria may be combined with other functions--becoming a Bar-Gelateria or even a Bar-Gelateria-Pasticceria in which coffee, liquors, gelato and pastries are all sold under the same roof.