What actions did the First and Second Continental Congresses take?
The First Continental Congress organized a boycott of British goods. The Second Continental Congress declared independence from Britain.
The Continental Congress was called following the passage of the Intolerable Acts. These were laws Britain passed to assert control over their American colonies after the Boston Tea Party. Delegates were chosen by their respective colony's congress.
The First Continental Congress met in Philadelphia in 1774. They decided to have "Committees of Safety" enforce a boycott of British goods. They also agreed to meet again in 1775 to consider changes in their response to Britain, and, somewhat secretly, agreed that each colony should begin preparing a militia in case of war.
Between the two Congresses, Britain refused to repeal the Intolerable Acts, even though the boycott was extremely effective. In April of 1775, British troops were sent to capture weapons being stockpiled in Lexington, Massachusetts. The Patriots got word of the troop movements (from Paul Revere's famous ride) and organized to meet them. British and Patriot troops battled in Lexington and nearby Concord (I won't go into the details of the battle here).
The Second Continental Congress met for the first time in May 1775, right after the battle at Lexington and Concord. Because of this, the Congress assumed management of the war. For the next two years, they became a makeshift government for the new United States. Here's the most important things they did:
They appointed George Washington as the general of a "Continental Army" and allowed taxes to help pay for the army.
They began sending diplomats to France to seek aid in their war effort.
They sent an "Olive Branch Petition" (peace offer) to Britain (designed to be rejected), that was rejected, inspiring colonial citizens to join the Patriot cause.
The signed the Declaration of Independence, thought this wasn't until July of 1776, more than two years after the war had started.