I have some confusions regarding VSAM as I am new to it. Do correct me where I am wrong and solve the queries.
A cluster contains control areas and a control area contains control intervals. One control interval contains one dataset. Now for defining a cluster we mention a data component and index component. Now this name of data component that we gives creates a dataset and name of index generates a key. My queries are as follows-
I tried finding a simple code but was unable so kindly explain with a simple example.
One thing that is going to help you is the IBM Redbook VSAM Demystified: http://www.redbooks.ibm.com/abstracts/sg246105.html which, these days, you can even get on your smartphone, amongst several other ways.
However, your current understanding is a bit astray so you'll need to drop all of that understanding first.
There are three main types of VSAM file and you'll probably only come across two of those as a beginner: KSDS; ESDS.
KSDS is a Key Sequenced Data Set (an indexed file) and ESDS is an Entry Sequenced Data Set (a sequential file but not a "flat" file).
When you write a COBOL program, there is little difference between using an ESDS and a flat/PS/QSAM file, and not even that much difference when using a KSDS.
Rather than providing an example, I'll refer you to the chapter in the Enterprise COBOL Programming Guide for your release of COBOL, it is Chapter 10 you want, up to and including the section on handling errors, and the publication can be found here: http://www-01.ibm.com/support/docview.wss?uid=swg27036733, you can also use the Language Reference for the details of what you can use with VSAM once you have a better understanding of what it is to COBOL.
As a beginning programmer, you don't have to worry about what the structure of a VSAM dataset is. However, you've had some exposure to the topic, and taken a wrong turn.
VSAM datasets themselves can only exist on disk (what we often refer to as DASD). They can be backed-up to non-DASD, but are only directly usable on DASD.
They consist of Control Areas (CA), which you can regard as just being a lump of DASD, and almost exclusively that lump of DASD will be one Cylinder (30 Tracks on a 3390 (which these days is very likely emulated 3390). You won't need to know much more about CAs. CAs are more of a conceptual thing that an actual physical thing.
Control Intervals (CI) are where any data (including index data) is. CIs live in CAs.
Records, the things you will have in the FILE SECTION under an FD in a COBOL program, will live in CIs.
Your COBOL program needs to know nothing about the structure of a VSAM dataset. COBOL uses VSAM Access Method Services (AMS) to do all VSAM file accesses, as far as your COBOL program is concerned it is an "indexed" file with a little bit on the SELECT statement to say that it is a VSAM file. Or is is a sequential file with a little... you know by now.