Dear Shri Raje Gowdre!
There are two types of LC, one is known as Foreign Letter of Credit (FLC) and 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 import of material from a foreign country, normally opened, for a particular order for one operation till the order is fully executed. Somebody has already gave some details which you can verify,
The other one is LC for Indian suppliers, it will be having a value ceiling for presentation of each bill valid for a period decided by the owner. In this case, the supplier whenever raises the bill, submits the bill, and the LR cto the bank in which LC is opened and he gets the money immediately. The banker will debit the amount from your account based on your authorisation which you have to give at the time of opening of LC. This is something like you are creating an ATM card to the supplier. The formalities require execution of some bond on stamp paper authorising 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.