IDENTIFICATION DIVISION is used to establish the Identity of the program, and assigns a unique name to the Program.
ENVIRONMENT DIVISION tells the environment – SOURCE-COMPUTER and OBJECT-COMPUTER on which the COBOL Program would run. It also declares the Input and Output file-names, accessed by the COBOL Program.
DATA DIVISION is the place in the COBOL Program, that creates Storage areas(COBOL Variables) for storing Data. Generally, COBOL Programs read data-records from Input-File, or Write records to Output-file. When the data-record from the Input-file is read, there's got to be a place in the COBOL Program, where the Input File Data arrives, its received and it has to be stored. COBOL Programs may do some rough-work. Such variables which act like a temporary scratch-pad, where you could do some rough-work, and which are there only as long as the COBOL Program runs are called WORKING-STORAGE Areas.
PROCEDURE DIVISION is the starting-point of the COBOL Program, where the Program begins to run. You code the Instructions that you to perform one-by-one in the PROCEDURE DIVISION.