What the programme is, why a channel is reviewed, and why the current requirements must be read from official pages.
The YouTube Partner Program is the programme through which a channel can be approved for certain earning features on YouTube. This article is independent training material. It does not describe the rules, which belong to YouTube and change.
It is an application and review process. A channel that wants to earn from features such as advertising applies, accepts programme terms and is reviewed by YouTube. Approval is not automatic and nobody can promise you an outcome.
In concept, three things are looked at:
The three areas fit together like this.
Advertisers want to know where their ads appear, and rights holders want assurance that earning channels respect their work. A review is how the platform tries to balance both. It also means a decision can be revisited if a channel's content or behaviour changes.
Ads are one way a channel can earn. Other features, such as memberships and similar tools, may or may not be available to a channel depending on its status and country. Treat each as optional, and do not build plans around a feature you have not seen in your own Studio.
For revenue concepts see RPM versus CPM, and for a full walk-through take the Monetization course.
Requirements, features and terms are set by YouTube and can change. Read the current official page before you act, and do not rely on any summary, including this one.