its not that easy ....
most of the times people use 3306 port to tranfer data from webs ( in case that website is hosted on other mashine ) ...
if not at first place you will need to find the right port ;)
it will not be that dificult , you can ping your ip on many ports and check if responds back , or google "open port checker" etc...
the next step i quess is to find vulnerable shits on their system that may grand you easy access on their database....
thats the dificult part , but you can try some shitty programs like Acunetix...
from now on , if yout knowleque is low you can use Havij and if you are lucky you may take access on their database ;)