Bank Guarantee Process for Accounting

HI ALL

CAN SOME ONE PLEASE EXPLAIN THE PROCESS OF BANK GAURANTEE

i;e  THE BANK ASK FOR 25 % MARGING AND 75 % FUNDED BY BANK  WHAT EXACTLY IT MEANS 

SECONLY THE SAY ITWILL BE EPT AS FD FOR THE AMOUNT AND WILL EARN INTEREST 

WHAT IFTHE BG IS UNPAID AFTER EXPIRY  WHAT WILL BE ENTRY FOR REVERSAL OF 25 % MARGING AND FOR THE FD INTERESRT EARNED

LETS SAY BG AMOUNT IS FOR RS 100000 AND I HAVE GIVEN 25 % BANK MARGING