Like Jno says, it is much simpler than most capital city metros. If you know where you need to get on/off you don't need to speak or understand. It was 1 euro flat fare for all journeys last time I was there - about 3 years ago. Most lines interchange at Termini, the train station - look out for pickpockets and aggressive begging, also be aware that buskers try to pick out compliant tourists and extract money in the actual carriages.
Depending where you want to go, bear in mind no metro stations anywhere near the forum or vatican.
buses are reputed to be cheap, easy and full of pickpockets.