The City of Heroes UI is packed with information, but it's designed to be intuitive. At the top left, you'll see your Health and Endurance bars, along with your target's health. Below that are your Power Trays, where you assign and activate your abilities. The main chat window is usually at the bottom left, displaying system messages, team chat, and global channels.
On the right side, you'll find your Mini-map, which shows your current location, mission objectives, and nearby contacts. Below the mini-map are various UI elements like your Team Window (when in a team), Mission Tracker, and Buff/Debuff icons. Pressing Esc opens the main menu, giving you access to Options, Inventory, Powers, Contacts, and more. Take some time to explore each window and customize their placement and size to your liking. A well-organized UI can significantly improve your gameplay experience.