am i finding the subnet mask properly?

Am i finding the subnet mask properly?

Please let me know if I am thinking about this (conceptually) the right way.

Internet Service Provider supplies you with a given network address.

Let's say: 192.68.40.0/27

I would calculate the subnet mask of this network using the following method?

11111111.11111111.11111111.11100000 (128+64+32 = 224)

So, the allocated network IP's subnet mask is:

255.255.255.224 ?

Is this pretty much how the process works?

The ISP says you can have xxx.xxx.xxx.xxx/xx "Network"?

and then you calculate your subnet mask from that?

Once you have your subnet mask, then what?

LOL

It's not the math that confuses me. It's not seeing "the purpose" behind the math that confuses me.