C Sharp is a programming language and it has a lot of features. Some of these features are implemented in the language itself while others are provided by libraries. Attributes in C Sharp provide you with a way to alter the behavior of your code.
Terminology. Mental model: An attribute is a variable that is stored in an instance or class. A method is a function that is stored in an instance or class.
A field is a type-independent variable defined directly in a class or struct. Fields are members of the type that contains them. Instance fields, static fields, or both can be found in a class or struct. Instance fields are unique to a type's instance.