There are four things you can do with an object in your inventory: Drop it, Get Info on it, Throw it, and Use it. All of these things are listed in the "Inventory" menu. For example, to drop your lantern, select it in the Inventory window, then pull down the Inventory menu and choose Drop. The lantern will disappear from the Inventory window, and will land at your feet (where you can't see it). The "Pick Up" button will become bright, to show that there is now something at your feet which can be picked up.
(As a side effect, the lantern always goes out when you drop it; that's why the "Scarab of RA" window suddenly turned dim and gray. Most things are unchanged when you drop them; the lantern is one of a very few exceptions.)
If you choose Get Info instead of Drop, a line will be printed in the News window describing the item you selected. Most of the time this won't tell you anything you can't read in the Inventory window, but for some objects (such as the lantern) you can learn something new.
Choosing Throw is like choosing Drop: the selected item will disappear from your inventory and appear on the floor of the maze. But unlike Drop, throwing an object may damage it when it lands, so be careful what you throw. You'll be asked how far you want to throw it; the distance is measured in "steps". That is, throwing something a distance of 2 will leave it in the same place as if you had stepped forward twice and then dropped it. How far you can throw something depends on how heavy it is.
Your final choice is Use. Different objects have different uses. For example, if you Use the lantern when it's on, it will turn off, and vice-versa. Some objects have no use; some are only useful at certain times or in certain places or situations. Since Use is probably what you'll do most often with the things in your inventory, there is a short-cut: just double-click on the object in the Inventory window.
