how to make a recommender system
The principles behind basic recommenders are often quite simple, although the implementation (i.e. building them and getting them running in real life) can quickly get complicated. More recent approaches are specialised areas of data science. Here are some simple guides to how to make recommenders.
Banik. Hands on recommendation systems with Python. 2018. Library resource
Google. Course: recommendation systems
Sharma. Aditya. Beginner tutorial: recommender systems in Python. Datacamp. 2020