Time to get out the ole Mark I recording and documentation device (Paper and pencil!) and sit down to figure out your requirements. I would suggest that you start with the design of the database and then move onto the programming requirements...
i made my project in vb.
i just want to make an database which have information of how many products are available in supermarket.
and it should be shown that when a customer purchase any product it should be deducted from the database.
Here(even in most of the site) we don't provide full developed software/Source code. This is to see your effort used to make/develop that software first. We might correct your codes if your code return any errors. It is not that we are unwilling to help you but we must follow the Rules and Regulations of Posting.
1. Which Database you want to use?
2. Which programming language suits your requirement( but you must also have good knowledge about that Programming Language)?
3. What are the datas(Data types) you want to store in your database?
4. How you want your software to work?
Above are some examples which you must think before developing your software then start writing codes.
As everybody else here stated, you need to put all your plans to paper and believe me when I tell you, PLAN PROPERLY. We have all made the mistakes of rushing into coding, only to find out halfway through the application that everything is a cock up. Funny enough, by that time you actualy do have the time on hand to start planning and re-write ALL the codes AND database.
Start with your database setup first and progress from there.
I have attached a small little data app that will help you in the basics of what you are planning to do.