how do you advertise your business on facebook?

Set up a Facebook page for the business if you don't have one, then run the ads from Ads Manager, not the Boost button on a post. Boost is easy but gives you far fewer options and tends to optimise for likes. In Ads Manager pick the objective that matches what you want (leads, sales, traffic), set a small daily budget and leave targeting fairly broad, apart from location. Make three or four different creatives so you can see which one works. Install the Meta pixel on your site before you start, or you won't know which ads brought in sales. Then give it a few days before you judge anything. People change everything after 24 hours and never learn what worked.