Views are different depending on where you sit in a London theatre. The Stalls are usually on the ground floor, and offer the best, closest views of the stage.
The Dress Circle or Royal Circle is usually the middle level, or top level in smaller theatres, and gives you a top-down view of the stage, which is great for musicals and big dance numbers. Boxes are usually located at Dress Circle height.
The Grand Circle is typically the highest tier in the theatre, but you can usually access seats at great prices. Be aware that legroom may be limited in these sections.