Depends a lot on the job.
Most likely avenue for a lot of people is starting off doing the job for an established business and then once they’ve got a good resume and body of work they can point to go freelance from there. This may also involve taking clients with them or even getting work from the previous business on a freelance basis (eg you start working as a graphic designer for a company, you leave to explore options or are fired because they dont want someone full time etc, and so you may pick up work from them).
A freelance creative would likely produce a work or a portfolio, then approach a publisher or wherever that work is generally used.
A lot of areas you may pick up an amount of work by personal referrals early on, one person is happy so they recommend you to friends and family (think a freelance wedding photographer – you do a couple of big weddings, those people post your stuff on Facebook with credit, thats reaching a decent audience already).
How much to charge is tricky, depends on supply and demand, and is something I see creative folks struggle with more (as i think other professions tend towards just having an hourly rate). But a starting point is often looking at what others are charging in your field as a starting point, maybe undercutting a little if you can afford to while starting up, then raising prices if you get plenty of work.
Taxes you just pay according to your local tax law. I dont mean to make this sound simple, its often not, but its incredibly area specific. For some simpler cash flows you may be able to do taxes yourself, especially if you have some advice from someone else in the field, but for most people you probably need an accountant, at least for the start up, to talk you through the different systems.
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