The short answer
Vesting means you have earned the right to buy your options, not that you own shares yet. On the vesting dates the options become yours to exercise, usually after a one year cliff and then monthly or quarterly over four years. You still have to exercise (pay the strike price) to turn them into shares, and until the company has a liquidity event those shares are usually impossible to sell. So a vested ESOP is a right, not cash. Read your grant letter for the cliff, the schedule, and the exercise window if you ever leave.
A curated summary to orient you, not advice. The resources below are the real value.