postage fees

Hi i need some informaiton regarding cheap postage in australia. i sell mobile phone accessories like cases, earphones, combine items etc which are not very heavy. they all in very light weight and everytime australia post charge me 6$ or 7$, which is no good at all. if i sell an item for $9.99, i am not getting any profit after postage packaging and cost price.

I heared of postage stamps or tickets can be used for such cheap posting.

i need to know how to use these stamps?

do you need to go to post office?

can you just stamp these on the package ans left in Post office box.

please help me out with the cheap postage.

regards