SAN FRANCISCO — As Apple prepares to show off new features for the iPhone and other devices at its developer conference on Monday, the company is grappling with an uncomfortable issue: Many of its existing features are already too complicated for many users to figure out.

At last year’s conference, for example, Apple’s top software executive, Craig Federighi, demonstrated how users could order food, scribble doodles and send funny images known as stickers in chats on its Messages app. The idea was to make Messages, one of the most popular apps on the iPhone, into an all-purpose tool like China’s WeChat.

But the process of finding and installing other apps in Messages is so tricky that most users have no idea they can even do it, developers and analysts say.

DoorDash, a food-delivery app that Mr. Federighi displayed on stage as a model of the new feature, dropped its Messages app for group orders a few months after releasing it because it drew little interest.