how to start business

i want to sell a product for a niche market. how to go about?

e-bay might be the easiest even though it is becoming harder to find things etc. is one way!

so what was it you were going to end in another thread here?

Technology! so you have proof of concept by now? or is it still in the design stages?

^ No if OP is read to sell it should better be far more than proof of concept.

Either way if its all tested and ready to deliver state, you have to find the right market. will online suffice or you think it should be somewhere in retail store? If online can you hit amazon as a independent seller or do you want your own online store (website). And then after setting up the website or account, you have to start spending $$ in advertising it. The quickest advertising is social media.
If you dont want it online at all, then you have to start making a list of stores whom you can pitch and give a demo of your POC.

Now going further back if you dont have it ready yet at all then make sure you have a solid POC as well as answer to the ten thousand questions that the investors and retailers will be asking. You tell us more and I'm sure we can discuss it further. Good luck

Online medium is powerful. Amazon, Ebay, shopify are few best options for you.
Media buying (Google ads, quora, pintrest, facebook, instagram, twitter, youtube) can cost you but if you really know your audience and able to laser target then it is really beneficial.

It is really good to know that you know your product and niche market. Your next step is to form a company, apply for tax number , brand and package your product and advertise in your niche by using available options.

even I want to sell a beauty product which I have made myself :D but unsure of the marketing

it needs marketing first, then it can be introduced

Niche market? Let's discuss the niche market!

You need to give more information about what is the product, also do some research on the demographic, and see the cost to sell ratio with three scenarios (good, bad, and the worst)

Do some field research for field and market work.