A Model represents a Single Entity of your project. If you already know SQL then you can compare it to columns. The mail difference between a Single Record vs Multiple is weather it could hold a single record or multiples.
For example if you are starting an e-commerce project the common models are mostly Products, Orders, Stores, Users, Carts, Reports etc. If you are designing a library management application the models are most likely to be Books, Authors, Profile, Booking etc.
But you are building api for a website or a landing page then it's better that you check
Single Record checkbox while creating a model.