use of DB in S7 300

Hello friends
PLZZZ help me how to use DB in S7 300 siemens PLC.

Thanks

What exactly do you need to know? If someone over here should ask a question as open as this, I would advise him/her to take one of my classes. There's no way to answer a question as open as this on a forum, only in a classroom, given you take a class long enough to cover the matter.

basically DB is the data block in s7-300 there are many blocks i.e FB etc... you should read the manual about these blocks

Hello usman;
In one of your earlier posts, you mention you are in a plant with one or two S7-400 CPUs. I must suggest you look at the blocks that are programmed in the PLCs to see how they are being used.
Very briefly (as you already were pointed to many excellent sources of information on previous occasions)a DB is a block of organised data that the programmer can create and use to store and retrieve information he needs for his program blocks.
Hope this helps,
Daniel Chartier