the short answer
To start an online coaching business, pick a specific niche, package your coaching into a clear priced offer, choose a platform that delivers programs and takes payment, win your first client through your network and referrals, then deliver an excellent result and turn the parts you repeat into a system.
This article is general information for coaches, not legal, financial, or medical advice - registration, insurance, and certification rules vary by country and change over time, so verify the specifics for your situation.