Last year, Apple added trackpad support to the iPad lineup, which naturally has its own list of gestures.
Here's our guide, complete with animated images, that explains it all. For example, you can have multiple apps open on the same screen, or multiple windows of the same app open at the same time, but you'll need to know how to make that happen. On the iPad, the entire lineup, regardless of whether or not it has a home button, relies heavily on gestures for multitasking and navigating the interface. The iPad's app switcher is pretty darn cool.
If it's been a while since you last updated your phone, the first thing you'll need to learn about using a newer iPhone is how to get around without a home button, which Apple removed in the iPhone X ( $400 at Amazon).