Network subnetmask

Hey!

I'm currently self-learning Cisco, but the book is pretty fuzzy about "subnetmasks".
See, if I am to for example create a subnetmask that allows me 14 networks for a Class-C network, do I write a subnetmask like 255.255.255.0, or am I allowed to write it like 255.255.240.240 (also is this a subnetmask that allows me 14 networks?).

Many thanks!

Class C address use the first 3 bits as the indicator. The following 21 bits are used as for network ID. The last octet is used as for host ID. So when you do subnetting for class C you will be fiddling with the last octet. 240 or 11110000 gives you 4 bits for subnetworks and 4 bits for hosts. So you do get 14 functional ips for each of the 14 subnetworks.

Someone correct me if I'm wrong.