K3 on a tourist visa?

[Seraphina]

Hello!
I need some assistance and guidance as to how to go about doing this. My partner is a US citizen and I am a citizen of Australia, in October we plan on marrying when I fly over to the US for the 3 week trip and ill be leaving to head back to Australia by the trip's end, I intend to head back to my country and fill out the necessary forms to be able to live in America with my partner.
I would love to know the first steps in the process of doing all of this as i am confused. I wanted to know that its perfectly legal to do it this way since I intend to marry and still return home? what are the necessary paper works I would need to fill out when I get back to? when going through customs, is it better to tell them I have intent on marrying and do I need to have paperwork to prove ill be returning back to my country?
I would love some clarifications on how to do this and important information I should know beforehand.

thank you!

[daggit]

You can get married on a tourist visa, and it is perfectly legal to state so to a CBP officer at entry. Once your 3-week trip is over, your partner files the I-130 petition for a spousal CR-1 visa while you await an interview in Australia.

Review the Family based Green Card section under the "Green Card" tab at the top.

Edit: I forgot to mention K3 visas are practically obsolete and basically are no longer issued. You would be issued a CR-1 visa after a successful interview.