The area called Plaka is the northern skirts of Akropolis hill, limited by the Ancient Agora, Ermou street, Filellinon street, and Amarias Avenue. Plaka is full of shops and restaurants for tourists, but if you look carefully, you will notice here remain old aspects of Athens. It is agreeable to walk around this area watching the Akropolis and many neo-classic buildings.
The restaurants in Plaka are mostly targetting tourists. For this reason, the price is higher (not necessarily unreasonable considering the high rent) and the food isn't always top notch. However, as it is quite agreeable to be seated at tables alongside the streets and among the old buildings, there is no reason to avoid to eat here. You can count on English menu, as long as you eat in Plaka.