The moment someone starts their own company, nothing much happens. They still work, and sell their work for money. The interesting transition points are in my opinion
- accumulate enough 'capital' (that may be in the form of software written) so that a sizeable part of the income is in fact rent on this capital
- Hire workers and sell their work, thus extracting surplus value
ETA:*: In response to the claim that capitalists "are employed by their customer":
This is very wrong , with a kernel of truth. The wrong: Customers don't hold the same kind of power over a capitalist as the capitalist does over their employees. The kernel of truth is of course, that capitalists are stuck in a rat race against other capital and compete for the same market. But they have options: exploit their workers harder (e.g. invest in machinery that allows the same worker o produce more), move their factory to aplace with lower wages or even liquidate and invest the money in a more profitable ndustry. The key difference between capital and workers beeing that capitalists can move capital, while workers can only move themselves, sometimes.
Claiming that capitalists are employed by their customers is more ofcustating than telling.