Entity methods work with small parts of the object model in order to read data from the database or write data to the database. When you create an entity method, you only need to enter the table and column name and, if required, a filter condition (WHERE clause). Internal processing is handled by the API Server. The data schema for the input and output also has a specific format.
For examples for the definition of entity methods, see the SDK under Sdk01_Basics\01-BasicQueryMethod.cs.