How startup stock options work, from the job offer to the day they pay

A startup can be sold for millions of dollars, and its first employees can still get nothing. Your part of a startup gets smaller at every funding round. Yet that smaller part can be worth more each time. How can both be true? Start with a job offer of 50,000 stock options, and go all the way to the day the company is sold. You learn shares, dilution, valuation, the strike price, vesting, exercising and the liquidation preference.