Made my first Sale. Need help with shipping.

Hello there,

I made my first sale today of a pokemon card.

I have been provided the shipping label from ebay for free ($10 more profit :) ) but need confirmation on where I can and can't put it.
Can I just stick it on a random letter and put it in a mail drop off? Or do I need to do a specific letter from the post office.

PS. I'm in NSW using Aus Post and the shipping arrangements are shown in the image.

Thank you, would love some assistance.

https://preview.redd.it/keptjk4xsoee1.png?width=449&format=png&auto=webp&s=e97fb1b0e4a74b541343e645c13ec297bc0065ee