Dear Shri Raje Gowdre,
There are two types of LC: one is known as Foreign Letter of Credit (FLC), and the other one is Letter of Credit for Indian suppliers. If you can be specific on the issue whether you want information about FLC or LC, the same can be clarified.
Broadly, FLC is for the import of material from a foreign country, normally opened for a particular order for one operation until the order is fully executed. Somebody has already provided some details which you can verify.
The other one is LC for Indian suppliers. It will have a value ceiling for the presentation of each bill valid for a period decided by the owner. In this case, whenever the supplier raises the bill, they submit the bill and the LR to the bank in which LC is opened, and they get the money immediately. The banker will debit the amount from your account based on your authorization, which you have to give at the time of opening of LC. This is somewhat like creating an ATM card for the supplier. The formalities require the execution of a bond on stamp paper authorizing the banker to deduct the amount from the account as and when the bills are presented by your supplier.
Please clarify which LC opening details you want.