To ask how you tube works re advertising

[Summertimesummer]

So, say if I was to post videos of myself eg playing the violin, and was lucky enough to get tons of views, how does it work re companies wishing to advertise before your posts? Do they contact you?
Also, do they pay you?
Thanks

YouTube supplies the ads. You have to be a ‘partner’ before you get any of the money. That requires you to have a certain number of subscribers and views.

If you get enough viewers/subscribers you can select to monetise your account. Advertisers pay youtube directly and they put the adverts on the videos.

You would need to have 1,000 subscribers and 4,000 watch minutes to get into their partner program. You then get paid for ads in the video.

You could also use affiliate links to say, violins, in the description box.

You could also get sponsored by a company, say a violin company, to promote their new violin.

Thanks so far.
Catswithflamingos- great advice. Thanks

As PP said 1000 subscribers and 4000 hours of watch time in the last 12 months get you into the YouTube eligibility and payouts depend on your niche and other factors as to how much you get paid for your views. For #ad type things, companies can reach out, there's sites to pitch to companies and people reach out independently and some people do affiliate stuff with amazon in the links.
A one off viral video isn't great if you're wanting to make money as won't be in the threshold for joining YouTube for monetisation and ditto external advertisers.