One is a widely-used, platform-independent, object-oriented programming language often employed for server-side applications, Android mobile development, and enterprise-level software. The other represents a mobile operating system developed and distributed by Apple Inc., primarily for their iPhone, iPad, and iPod Touch devices. The former facilitates cross-platform deployment, while the latter operates within a closed ecosystem characterized by stringent app store guidelines.
The value of understanding their relationship, or lack thereof, resides in the ability to develop diverse applications. While applications for one do not directly run on the other, web services and APIs crafted using the first language can effectively serve data to native applications on the second platform. Historically, developers might leverage shared business logic across different platforms through such architectures.