joed pretty much summed it up.
im curious why you dont ask the family electrician...
it's OK to do the job yourself, provided this is on your home and you pull the required permits.
it is advised to have a skilled electrician do the job, but not a requirement
1- a double pole breaker(not to exceed 90% of the main breaker size)
2- a length of 4-wire to run between the Main and the Sub panels (size depends on Amps)
3- likely a few Neutral bar adapters to accomodate the larger neutral and ground wires
4- No Al Ox if you use Aluminum wire (prevents oxidation)
5- a few odds and ends such as wire clamps, brackets, staples, etc.
6- obviously a new sub-panel
7- safe and adequate space to mount the new panel
if you're asking because of cost... the materials should run under $200 plus a case of beer for the electrician