Question : what does the TCP/IP submask perform

I'm building a small ofice network without a server, as they have a proxy server to access Internet we are using TCP/IP so I got interested on the use of the submask.

Can I section the network by changing the submask number?
Would I lose the printer atached to an external server?

Answer : what does the TCP/IP submask perform

It may be a pain, but the only way to understand network masking properly is to convert all octets to binary.

An IP address is made up of 4 sets of 8 bit numbers, so an IP address of 192.168.10.1 translates to binary as 11000000.10101000.00001010.00000001
If we apply a subnet mask of 255.255.255.0, this translates to binary as 11111111.11111111.11111111.00000000 and is a 24 bit subnet mask.
This means that the first 24 bits of the IP address (indicated by 1's in the subnet mask) are known as the network address, and the last 8 bits (indicated by 0's in the subnet mask) are the host address.
This would mean that you could have 254 clients on that subnet, from 192.168.10.1 to 192.168.10.254 (you cannot use 0 and 255 as 0 is the network address and 255 is the broadcast address).
If you have less client machines to run on a particular subnet then you may choose to use a different subnet like a 28 bit one 11111111.11111111.11111111.11110000 which is 255.255.255.240 which will leave you 14 host addresses 192.168.10.241 to 192.168.10.254 (you cannot use 240 or 255).
And I'm sure you can see now that if you had a large number of clients on one subnet you may choose to use a smaller network mask like a 16 bit one 11111111.11111111.00000000.00000000 which is 255.255.0.0 this will give you 65534 host addresses 192.168.0.1 to 192.168.255.254

The advantage of subnetting is that it reduces traffic on the local subnet and can speed things up. In the example of having 65534 clients on the same subnet, the number of collisions and dropped packets will be very high, while a small network will run faster with less collisions.

The disadvantage is that you will need to route between subnets, requiring a router which can get complicated.

The choice is yours.

If you are currently using a 24 bit subnet mask you may want to subdivide that into, say, 4 subnets for different departments each having a 26 bit subnet mask 11111111.11111111.11111111.11000000 or 255.255.255.192 giving you 4 address ranges :
192.168.10.1   to 192.168.10.62
192.168.10.65  to 192.168.10.126
192.168.10.129 to 192.168.10.190
192.168.10.193 to 192.168.10.254

If you have trouble calculating decimal to binary and back then the calculator you get with windows has a scientific view which will convert for you (only work on 1 octet at a time though).

As far as the printer goes, it is still possible to use a printer on a different subnet as long as your routers are set up correctly.

I hope this has made things clearer