What is the most important event that happens at a party's National Convention?

During a national convention, political party members gather every four years as all of the states participate. The convention is held in the summer prior to the presidential election. Since they represent the state’s voters, state party sends representatives to vote for the candidate favored in their state. When they have selected the President and Vice President of their party that is when the convention comes to an end. During this period the party prepares their platform or list of ideas as well as their stand on important issues affecting the country.