An entity defines any person such as student, teacher; place such as classroom, building; thing such as computer, lab equipment; concept such as course, attendance for which data will be collected.

Attributes are one of the building blocks of relational database design that define the additional characteristics or information for an entity.
For example, name, gender, address, salary, years tenured can be the attributes of teacher entity.

A relationship is a logical linkage between two entities that describe how the entities are associated with each other.

There are three relationships possible between two tables namely: one-to-one, one-to-many, many-to-many.

The most important classification of a relationship is called its cardinality. The cardinality of a relationship allows the database modeler to specify how instances of each entity relate to each other. The three major cardinalities are: one-to-one, one-to-many, many-to-many.