If you have finished your amazing manuscript and want to start on the path of traditional publishing, you are likely to want to try getting an agent first.
Most of the well-known publishers, and certainly the big five, simply DO NOT ACCEPT submissions from authors directly. The agent 'barrier' is a way for publishers to have an extra checkpoint, and a further layer of editing and proofing, which reduces their costs and helps get their current list into publication faster. The agents know what the publishers are looking for and help winnow out more books that may not sell.
It's not a perfect system, nor even a very good one. Agents have hundreds of submissions to go through each month, and will likely be making snap decisions based on a few sentances in your query letter. If it doesn't feel quite right to them, or if they have other authors with the same types of stories, they are going to say no. It doesn't matter how good your story is, how glorious the righting, how important the themes; your manuscript is in the slush pile. The vast majority of your queries to agents will not even be answered, and its possible that few will even read your first chapter let alone request the full manuscript.
For Australian authors and indeed any writer not in the UK or the USA, you have another whole barrier to entry. There are just fifteen (15) agents listed as members of the Australian Literary Agents Association. You can see the full list here. Some of these overlap with the seventeen (17) listings on Query Tracker, but only 5 of these are currently accepting submissions. If you have a genre fiction (Sci-Fi for example) there are currently no Australian agents accepting submissions, and few are accepting children's books or even YA!
If your book is set in Australia, then you should probably try the Australian agents first as they will understand the setting and know about the publishing prospects. If not, or you've already tried this, you will need to look at US- or UK- based agents. Generally Australian authors should consider London-based agents first as the you will likely be writing with British English spelling.
An agent may well be considered a necessary evil. However they will have your back; they don't make money until a book is published and sold and they will negotiate on your behalf AND manage your writing career. The good ones will help you navigate book fairs, speaking appearances, launches and social media. Yes, they are indeed the ones with the power when you've finished your manuscript and want to publish, but they are also reliant on authors for their livelihood and are on the lookout for your amazing work.
1. Get your query letter checked; Fiverr have some good editors who know what they are doing, check with other writers on facebook and twitter groups, or pay for a professional opinion through Manuscript Academy or Reedsy
2. Have Beta readers critique your manuscript; there are other writers in various Facebook groups who will be up for swapping manuscripts for this purpose. After a few rounds of Beta readers, go the professional route again and get a pro editor to give you a critique. The first chapter is the most important; get it perfect before you send it!
3. Sign up to Query Tracker; the full price is about $30 per month which is worth it for the comprehensive list of agents and as a great way of keeping track of your submissions
4. Read the submission guidelines for each agent and follow them carefully. There are loads of stories from agents about receiving emails on manuscripts in genres they don't accept and you are wasting your time and theirs. If you submit when they have specifically said they are closed to queries, your email will go straight to the bin.
From the querying trenches....good luck!