A UDF is called by means of its function call in an expression, see "User Defined Functions (UDFs)".
When a UDF expects input parameters, the corresponding values (arguments) must be transferred to the UDF in the function call.
The (only) return value of a UDF is determined by the RETURN statement, see "RETURN - Supply the return value of a User Defined Function (UDF)".
The EXECUTE privilege for the UDF to be executed is required to execute a UDF, but not the privileges which are required to execute the DML statements contained in the UDF. In addition, the SELECT privileges for the tables which are addressed in the routine’s call parameters by means of subqueries are required.
When an expression is evaluated, the function contained in it is performed and then the replaced by the calculated return value.
UDFs can be called in views.