To open a demat account, you have to approach a depository participant (DP), an agent of depository, and fill up an account opening form. The list of DPs is available in the websites of depositories: CDSL (Central Depository Services (India) Ltd and NSDL (National Securities Depository Ltd).
Along with the account opening form, you must enclose photocopies of some documents for proof of identity and proof of address.
You will have to sign an agreement with DP in the depository prescribed standard format, which gives details of rights and duties of investor and DP. You are entitled to receive a copy of the agreement and schedule of charges for future reference.
DEMAT account Number
The DP will then open an account and give you the demat account number. This is also called beneficial owner identification number (BO ID). All your purchases / investments in securities will be credited to this account. If you sell your securities, your demat account will be debited.