If it's basically pass-through income from a business then you fill out (in the US) a Schedule C. And you do one for each business like that. And you also have to separately fill out the medicare & social security taxes, paying both the employer and employee side of it.
It sounds complicated, but paying about $100 for the TurboTax edition that handles small businesses will make it fairly easy. Yep, they've got strong regulatory capture in this space, but business income isn't always straight forward so I would consider ~$100 well worth it. Though I'm sure that some dead-simple home businesses really wouldn't need it.