“Cisco DevNet is Cisco’s developer program to help developers and IT professionals who want to write applications and integrations with Cisco products, platforms, & APIs” - Wikipedia
DevNet offers free learning resources (tutorials, courses, labs, etc.) to learn about network automation and network-based software development.
DevNet covers an enormous amount of information. Cisco even offers a certification program in DevNet itself, as well as in many of the topics and fields covered therein.
DNA Center Sandbox
Notably for those studying for a CCNA certification, DevNet offers a Cisco DNA Center sandbox to help you familiarize yourself with DNA Center.
It is important that CCNA exam-takers be familiar with DNA center as it is explicitly mentioned in the CCNA Exam Topics.