You will find varying levels of English spoken in stores and on the street. People are more than helpful though, and you should have no problem finding what you need.
Like most Italian towns, almost all stores will be closed for lunch. In Rocca Priora most stores are closed 1PM-4:30PM, but hours vary.
Rocca Priora's gelateria is only open during the summer. If you want Gelato, consider going to Frascati or another nearby town.
If you need a bank machine, there are at least three available. The one nearest the bus stop is by Credito Coopermativo del Tuscolo and does not accept international cards. Two machines that accept international cards (have PLUS Logo) are at the Post Office, and at Banca di Roma. The machines may be slow and the English questionable, and if you get an error try back later or the next day. They seem to give the same error message for all problems (machine out of money, card didn't read properly, etc).
The city is reachable by bus with the Cotral S.p.A. service. If coming from Rome, take Metro Line A to Anagnina (last stop in that direction). There will be an electronic departure board showing when the next bus to 'R. Priora' is, or simply walk to Platform 6 where it normally leaves from. You can download a timetable from the Cotral S.p.A. website, be warned the timetable for Rome is massive.
Tickets for the bus should be purchasable from a tobacconist, and if in Rocca Priora there is one almost opposite the bus stop. The bus stop in Rocca Priora is located drops off close to the main piazza.
You will need a 3-zone ticket which should be around 2 euro, good one-way only. Alternatively a day pass which is also valid on the Metro will be 6 euro. The bus stops in a number of other towns depending on the route (Frascati, Monte Porzio Catone, Montecompatri), all of which are interesting points to get out.
You can easily walk around Rocca Priora, but there is limited local bus service to get a bit further out. You are better using the Cotral buses and simply going on to another town (Frascati, etc).
There are no main attractions in Rocca Priora. But you might be interested in:
There are several stores in the area. There is several supermarkets (Sidis), fruit stores, snack bars, and other food stores for eating 'on the cheap'.
Every Thursday morning there is a large market, you can find a wide range of fresh food available. It occurs in the large parking lot beside the post office, and if you will be in town on that day is well worth attending.
Rocca Priora also has several pizza stores. You can find the wafer-thin roman-style pizza at XXX, which will require you to order a pizza for yourself. Or you can get pizza by the gram as elsewhere in Italy, which has thin crust but not the 'wafer-thin' type.
Using the Cotral buses, you can venture to many nearby cities and towns.
If planning on taking the train: the bus ride from Rocca Priora to Anagnina, Rome lasts 45-60 mins depending on traffic. The Metro ride from Anagnina to Termini takes 30 mins.