Hey @mooremike602,
I’m not positive where you are at in your studies so I’ll try to not make assumptions. However, as prescribed in mathematics binary is a base-2 numerical system, which uses only two symbols: typically “0” and “1”.
To start off, 192.168.0.0 /24 gives you the range of: 192.168.0.0 - 192.168.0.255. However, 192.168.0.0 /25 is half of that, or comprised of two subnet values: 192.168.0.0 - 192.168.0.127 and 192.168.0.128 - 192.168.0.255.
This means that you can fit two /25’s into a single /24. This holds true across the board - one could derive from that notion that as you shrink your prefix length (going from a /25 to a /24, or from a /24 to a /23) you will need two subnets to fill that gap.
So, if we carry that same logic over, we know that the network 192.168.0.0 /24 is from 192.168.0.0 - 192.168.0.255; the second subnet is from 192.168.1.0 - 192.168.1.255; the third subnet is 192.168.2.0 - 192.168.2.255; and so on and so forth.
In comparison, you can find the block size, or subnet range from determining what the bit value is left of your slash notation. If you are given a 192.168.0000000|0.00000000 /23, we know that left of that slash or hyphen is a bit value of 2; the bit values being 128 - 64 - 32 - 16 - 8 - 4 - 2 - 1 respectively. The hyphen is in-between the 2, and 1 bit value, and we know left of it is 2 which is our block size. We also know that our prefix length determines what octet we operate within, and because we are “borrowing” 23 bits (192.168.1111111|0.00000000) we work in that octet as such.
That said, this means that our first subnet range is 192.168.0.0 - 192.168.1.255 /23. This shows us that as we decreased, or shrunk our prefix length value by 1, the next largest value will require 2 subnets to fill it’s place. 192.168.0.0 - 192.168.0.255, and 192.168.1.0 - 192.168.1.255 is two different subnets that match exactly to our single /23.
In short, two /25’s can fit into a single /24; two /24’s can fit into a single /23; two /23’s can fit into a single /22; etc.
If there is anything I didn’t explain well enough, or you would like further clarification feel free to @ me, and I’ll do my best. Thanks!