An IP address is composed of two parts: the network prefix in the high-order bits and the remaining bits called the host identifier.
IP v4 gives you 32bit address space. IP v6 ives you 128bit address space.
201.1.1.0 -> Having a 255.255.255.0 address-space (class C /24) how many hosts can you have? -> 256 -2 = 254 (Because .0 and .1 are reserved)
Going away from hardcoded A,B,C classes CIDR introduces the /x notation to determine the subnet mask.
192.0.2.0/24 means that the first 24 bits are reserved for networking.
The IPv4 block 198.51.100.0/22 represents the 1024 IPv4 addresses from 198.51.100.0 to 198.51.103.255.