The "101" here is part of a fixed formula meaning "an introductory or basic course in some topic". Most usages would use it as a title, not part of a sentence, so the part of speech is unclear.
This usage of "101" comes from a naming scheme used in many US universities for naming classes:
- The subject the course belongs to
- A first digit representing the academic level, where "1" is the simplest / introductory level
- Additional digits to distinguish multiple courses at a similar level
Because US degree programs generally allow students to take a wide variety of courses, particularly in their first year, there are many courses which are an introduction to a particular area of study. These are assigned names like "Biology 101", or "Artificial Intelligence 101".
That has led to a popular usage (particularly in the US) of the template "Topic 101" as a short-hand way to say that something is a beginner's introduction of some sort.
Similar postfix labels are often used in product names, such as "Peugeot 208", "Chanel Number 5", or "Pimm's Number 6".