A heads-up display (HUD) is a two-dimensional user interface element that controls inworld elements, such as your avatar or animations. A HUD typically consists of a control panel with buttons that do certain things; you activate it by "wearing" it as you would an article of clothing. HUDs are created by Residents using LSL. For more information, see HUD.
HUDs are used in many kinds of products where information needs to be directly communicated to you. Popular uses include:
Books - HUDs are useful for viewing info that may be tricky to camera-zoom in on.
Combat systems and games - See your health, stamina, experience points, and other relevant in-game info. An HUD can be a whole game experience, similar to casual gaming in a web browser. (In fact, with Shared Media, an HUD can show Flash-based games.)
Customizable attachments - Click color swatches to change your hair, clothes, shoes, or more exotic accessories like neko tail and ears. Make particle effects (like fire and smoke).
Multi-tools - Gadgets that consolidate various practical functions in one HUD.
Vehicles - Use HUDs to display features such as dashboards with speedometers, gear indicators, and distance traveled.
Location - Shows a GPS position indicating where you are on the sim with the X and Y location on a map.
After you get a HUD (and unpack it if necessary), it appears in your inventory, perhaps in a folder (with notecard instructions and a landmark to the store it came from).
Right-click the HUD and select Wear to automatically attach it to the point the HUD creator set when they made it. If there are buttons, they may be labeled, and you can often safely explore by clicking them to see what they do.
Note: Any Second Life object can be attached to any attachment point. However, attaching something as a HUD that is not designed as one may not be very useful. For example, attaching a house object may show up as a big, wood-textured square that obscures your field of view.
Moving your HUDs
To move an HUD you're wearing:
Right-click the HUD onscreen (not in your inventory) and select Edit.
Drag the arrowheads to reposition the HUD.
The HUD remembers its position the next time you log in. In some circumstances (like a sudden Viewer crash), the HUD may forget its position, so use this workaround in addition to the above:
Right-click the HUD and select Detach.
Find the HUD in your inventory, right-click it and select Wear.
Reposition the HUD following the steps above.
If wearing one HUD makes another disappear
These HUDs are being worn on the same attachment point. To solve the problem:
In your inventory, right-click one of the HUDs and select Attach To HUD. You will see the list of attachment points and, in brackets, which HUDs are currently attached to them. Select an attachment point that isn't already occupied.
Reposition the HUD as desired using the steps above.