Kinshasa's restaurant scene is concentrated in Gombe, where you can eat well for most budgets. The DRC's national dish is moambe chicken -- a rich stew made with palm nut sauce -- and it appears on nearly every Congolese menu alongside grilled fish from the river, plantains, and fufu (pounded cassava). River fish, particularly capitaine (Nile perch) and tilapia, are a local staple and worth seeking out at any riverside restaurant.
Gombe has a reasonable selection of restaurants ranging from simple Congolese grills to Lebanese and European options catering to the expatriate and diplomatic community. Prices in the better restaurants are surprisingly high by regional standards -- Kinshasa is an expensive city. Street food is everywhere and cheap, but apply the usual caution about hygiene.