Basically you need this main things:
1. Product to sell (affiliate marketing)
2. An audience (a list of opt in subscribers)
You need a good product that can sell itself. Otherwise no one will buy from you. You also need to be honest and trustworthy like in all business dealings.
To get your audience you need to advertise and get traffic to your website.
Like all businesses you must have capital to invest. Without capital you won't have money for your overheads and products. Advertising also needs money.
All this being said. I need capital