You are allowed to drop leading 0's in each 2byte section.
2001:0770:0008:001A:0000:0000:0000:0001 becomes 2001:770:8:1A:0:0:0:1
You are also allowed shorten a consecutive group of 0's using ::
You are only allowed do this once per address so devices know how to expand the address again.
2001:770:8:1A:0:0:0:1 becomes 2001:770:8:1A::1
The CIDR mechanism is used to identify the network portion of the address.
2001:770:8:1A::1 has 64 bits assigned for the Network portion and 64 bits for the host portion. This is stated as 2001:770:8:1A::1/64