What are subnets ? And why are they good for me ? [HELP]

Hello BHW.
I don't understand what are subnets and why do I need them buying proxys ?
Searched Youtube and google and only found some complex stuff.
Can anyone help me to understand ?

Ex. If you buy 5 private proxies, the provider will allocate you proxies from 2 different prefixes (subnets)
that means that you will get 4-5 different ips ...

Ex. different c prefixes (subnets) :
1. 192.168.1.0 - 192.168.1.255
2. 192.168.2.0 - 192.168.2.255
and so on

when the provider is going to allocate the proxies and has told you that they will allocate from 2 prefixes (subnets) then you will get proxies (based on my example) from prefix 1 and prefix 2.