As IPV6 contain multiple headers, how does it know where particular header ends and next item begins?

Several headers types contain fixed size. For illustration a base header has a fixed size of exactly forty octets. To remove to the item subsequent base header, IPV6 software easily adds forty to the address of the base header. However some extension headers do not contain a fixed size. In that case, the header should contain adequate information to permit IPV6 to find out where the header ends. The following figure demonstrates the general form of an IPV6 option header.

The Ipv6 option extension header

Since the size of the options header can vary for one datagram to the other the HEADER LEN field gives the exact length.