That is a pretty sweeping question, but the short answer is:
 Get a website built correctly;
 Set up social media accounts at the platforms that your ideal clients would use;
 Connect the social media accounts to your website;
 Write articles on your website which your ideal clients would want to read;
 Mention the articles on your social media platforms;
 capture the names and email addresses of those who come to your website to read the articles, so that you have a constant source of prospective clients.
I hope that gets you started in the right direction, and if you need help with anything in particular, I would be happy to expand on the list above for you. Good luck with your online ventures, you absolutely NEED to have an online presence today, because your competitors certainly will.
I appreciate your time, efforts and I value your advice.
Thank you so much.
As with all things you would like to do that you have never done before, look at others that are very successful at it. Google buinsess brokers and find out who is doing really well, study what makes them great, and apply the same principles to your business.