GPS will tell you how to get to the nearest Apple store. With iBeacon, Apple hopes to guide you around once you’re inside, whether it’s to pick up an order, upgrade to a new iPhone or shop for a pair of headphones. On Friday, Apple Inc. will begin using the technology at its 254 U.S. stores to send you messages about products, events and other information — tailored to where you are inside, provided you have downloaded the Apple Store app and have given Apple permission to track you. Using the iBeacon feature, the app will notify you if the computer you ordered is ready to be picked up, for example. Show a clerk your screen with the order number, and the clerk will get it for you. Walking by an iPhone table? You may get a message asking if you want to upgrade, check your upgrade availability and see if you can get money for trading in your old phone.