Diamond Bar is a suburb of Los Angeles, around 30 miles east of LA downtown. You can take CA-60 East freeway from LA downtown. If you come from Orange County, especially Disneyland, please take CA-57 North freeway. However, both freeways have serious traffic congestion during rush hour.
The most major roads in Diamond Bar are Diamond Bar Blvd, Golden Springs and Grand Ave.
Diamond Bar is famous for "country style living", not too many shops around. However, you can find Target and Walmart in the city.
Nearly all popular fast food chains have their restaurants in Diamond Bar, e.g. McDonalds, Carl's Jr., KFC, Taco Bell, In-N-Out, Del Taco, Jack-in-the-box, El Pollo Loco. Due to high Asian population in this area (around 40% Asian), Asian restaurants can be easily found. Chinese, Korean, Indian restaurants can be found in this area too. Or you can drive 5 miles west to Rowland Heights, where you can find lots of Chinese and Korean restaurants there.