... for a newbie... the best way to describe the way a subnet works... and know how & why to change it... is as follows.
It's called a mask... because it is exactly that. i.e. what part of the address is important.
Computers understand everything as binary. So, I'll need to break it down a bit for ya.
ip address are 4-bytes separated by a dot to keep things simple. i.e. 188.8.131.52. If you write it as binary... it looks like:
The mask, like I said earlier, is what part of the address is important. i.e. 255.255.255.0 means:
Everything important is a 1... everything not... is a 0. More specifically, If the parts masked by 1s is the same, the address is local. Otherwise, it needs to be routed. (routing is a whole other subject... and I'm not going to touch on it)
so... in this example, as long as the address matches the first 3 bytes... its treated as a local address. (not a "loopback" address... but local to the subnet). So anything that starts with 10100000.01010000.00000001. or 160.80.1. is in the local subnet. Doing some simple binary math... you can see that there are 8 bits that can change and not affect the part that is covered by the mask. 8-bits means 256 values (0-255) Potentially there are 256 unique addresses in that block. 7 unmasked bits would mean 128 values... 9 would mean 512.
You can either expand or shrink the subnet... simply by adding more 0s or 1s in the mask.
255.255.254.0 = 11111111.11111111.11111110.00000000
255.255.252.0 = 11111111.11111111.11111100.00000000
255.255.248.0 = 11111111.11111111.11111000.00000000
Now... as has been previously mentioned by someone else... there is a difference between the number of usable addresses, and the number of total addresses. For each subnet... 2 addresses are reserved. 1 for the network identifier (the very first address) and one for the broadcast address (the very last). So... as previously mentioned... in a network with 256 address... there are only 254 usable addresses. 128 = 126, 512 = 510... etc.
With this simple knowledge, you can easily build your subnet mask to be as big or as small as you want. I do have some words of caution for you as well...
I noticed you are playing with a 184.108.40.206 network... This doesn't fall within any of the "blackhole" networks, which means potentially could interfere with whoever owns that IP block. If you cause them harm, they can take legal action against you. If you don't own that IP block, you shouldn't use it. There are 3 black hole networks designed for private use, that you can cut-up any which way as long as you keep within them.
I hope this crash-course will stick with ya... and start to open your eyes to a much larger set of concepts in networking. Feel free to pester me if you want to go any farther...