The Colonists were mad that they were having to pay taxes without representation. So when the tea was coming, The Sons of Liberty tried to get the Boston Mayor to stop the tea from coming into the ports.
That didn't work out in their favor and the tea still came in as scheduled.
The Colonists also asked the people working the ship and the tax collectors to just quit their job
That plan had also not worked out in their favor.
They then decided that the best way was to destroy the tea and they dressed up as Indians so if they got caught, the Indians would take the blame.
They snuck out at the dead at night when no one was watching the ships and dumped the tea out into the Boston Harbor.