Hello Minali
In the first case, the 0.0.0.0/1 subnet is all addresses from 0.0.0.0 to 127.255.255.255. This is the class A range of addresses. The le 27 keywords indicate that each subnet matched by the prefix will have a subnet mask less than or equal to 27. So this prefix list matches things like 10.10.10.32/27, 86.52.14.64/26 and 100.100.128.128/25 and any other class A subnet with a prefix less than or equal to /27.
On the other hand, the second prefix list is 128.0.0.0/2 which contains all addresses from 128.0.0.0 to 191.255.255.255, which are class B addresses. The ge 17 keywords indicate that each subnet matched by the prefix will have a subnet mask greater than or equal to 17. So this prefix list matches things like 132.0.0.0/17, 144.144.128.0/18, and 152.55.55.0/24 and any other class B subnet with a prefix greater than or equal to /17.
I hope this has been helpful!
Laz