What is Job and what is resource manager?



I was going through the lecture #32 of the course the instructor talks about Job and resource manager, I couldn’t understand these very well. Also, from the certification point of view, why we would need resource manager and look for the details in yarn-site.xml file?

All of this doesn’t make any sense to me. Either it is going too fast and at a very high level or maybe I need to have some background for this course?

The introduction of the components of Hadoop eco-system is at very high level. Is it too early to ask these questions and maybe they will be covered later in the course?

Any help/clarification is appreciated.