Apple unveiled its latest iPhone lineup today at the company's annual launch in Cupertino, California, where the tech giant also introduced a new Apple watch.

The event is an important showcase for Apple, which wants to spur consumers to upgrade their older iPhones in favor of its latest devices. This year is especially important given that the company is struggling to break out of a slump that's led to a sales drop in three consecutive quarters. 

"These are the best and most capable iPhones we've ever made," Apple CEO Tim Cook said at the Tuesday event.

Here's what to know about today's event. 

What is new about the iPhone 15? 

Here are some of the changes announced by Apple on Tuesday:

• The iPhone 15 and 15 Plus will come in five colors: Pink, yellow, green, blue and black 
• The iPhone 15 Pro models will come in black titanium, white titanium, blue titanium or a natural titanium finish
• The Pro includes an A17 bionic chip that will improve speed and performance, according to Apple
• All models iPhone 15 models have the "Dynamic Island" for app notifications — a look that was introduced with last year's Pro and Pro Max devices
• The phone comes in two sizes: Either a 6.1-inch base model or 6.7-inch screen Plus model
• The iPhone 15 has an improved, 48 megapixel camera

When will the iPhone 15 be available for purchase?

The Apple iPhone 15 will be available for preorder on Friday, September 15, and will be on sale in stores on September 22.

What will the iPhone 15 cost?

Apple is keeping the price of many iPhone 15 models the same as the 14. 

• The iPhone 15 will start at $799, while the 15 Plus will start at $899, with 128GB of internal storage. That's the same price as for current iPhone 14 models
• The iPhone 15 Pro will start at $999, which is the same price as the iPhone 14 Pro, Apple said
• The Phone 15 Pro Max starts at $1,199, up $100 from the 14 Pro Max

Apple also said it will have "excellent offers" for consumers who want to upgrade, including up to $800 off when you trade in an iPhone 11 or newer.

Is the iPhone charger moving from Lightning? 

Apple is phasing out its Lightning port cables, which were rolled out in 2012 with the iPhone 5, because of a mandate from European regulators that all phones use the USB-C charging port starting in late 2024. 

Apple said its iPhone 15 and iPhone 15 Plus will have USB-C ports, but can also be charged with MagSafe, which is a magnetically attached power connector. 

The transition may not be too inconvenient for most consumers. That's because USB-C cables already are so widely used on a range of computers, smartphones and other devices that many people may already own them. 

The shift to USB-C cables may even prove popular since that standard typically charges devices more quickly and also offers faster speeds for data transfers.

What is new with the Apple Watch?

Besides its new iPhones, Apple introduced the new Apple Watch — a product that made its debut nearly a decade ago. 

The Apple Watch Series 9 starts at $399, while the Apple Watch SE starts at $249, Apple said on Tuesday.

One new Apple Watch feature is something called "double tap," a command users can deploy to answer calls or play or pause music with one hand. By tapping your index finger and thumb twice on your watch hand, the watch will respond to the gesture, Apple said.

The double tap gesture could be useful for someone walking their dog or carrying items, allowing them to send commands to their Apple Watch with one hand, the company said.

Should I upgrade my iPhone?

About 25% of Apple's 1.2 billion iPhone users haven't upgraded their phones in four years, according to Wedbush Securities analyst Dan Ives. Some of those 300 million people with older iPhones may be wondering if it's time to open their wallets and get a new device this year. 

Still, it can be tough to determine when it's time to retire your old phone and switch to the latest iPhone. Much of that decision could depend on what type of handset you currently use, with owners of newer models having less of a reason to upgrade, Olivier Blanchard, a research director at tech research firm The Futurum Group, told CBS MoneyWatch

"The company's products remain amazing, but with the innovation curve of the whole smartphone category flattening there just isn't much the company can do to distinguish each generation of iPhone from its predecessors when it comes to technical features, making price the critical variable in driving sales," Wall Street analyst Adam Crisafullo of Vital Knowledge told investors in a report.

But if you have a smartphone that's older than the iPhone 12, the iPhone 15's new chip, improved camera features and USB-C port could be a big step up. 

—With reporting by the Associated Press.

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