Despite its widespread presence in modern Japanese culture, curry is not an old Japanese dish but rather a fairly recent foreign import. Originally from India, it entered Japan via the British Royal Navy in the late 1800's. The British Royal Navy regularly served its sailors various curry stews which were both popular among the men and gave them needed vitamins, so the young Imperial Japanese Navy did the same. From the Navy it eventually reached a wide appeal among the general Japanese population.
Japanese style curry is typically composed of rice and curry sauce, often topped with a fried meat or mixed in with vegetables (or both!) It tends to be a bit more mild than its Indian predecessors, although I still think it has plenty of spicy 'kick' (admittedly, I'm not a huge fan of spicy food, so my definition of 'spicy' may be rather tame compared to others).
CoCo's has a standardized English menu at each of its locations (usually at the back of the menu stand at each table, but available upon request if it's not already there) with each main dish listed along with a picture, English, and Japanese writing, so there's little chance your order will be mixed up or confused. The main dishes tend to run from 600-1000 yen in price, although you can increase the portion size for an additional cost (the normal size has always been fine for me). Side items such as various salads are also available. Additionally, CoCo's is a nationwide chain, so if you get a hankerin' for curry or just want a place where you know you can read the menu, there should be one in the area. I've eaten at CoCo's restaurants everywhere from Shibuya, Tokyo to right outside Nagasaki Chinatown. My personal recommendation to order the curry topped with fried pork 'tonkatsu' cutlets. Skip the fried chicken nugget curry, those nuggets are usually too much fat and batter with too little meat (the pork cutlets are all meat). After you've finished eating, take your ticket to the cashier near the door to pay your bill, this is definitely a casual place. Bon appetite!