The Constitutional Convention was held on May 25, 1787 in the Pennsylvania State House, now known as the Independence Hall in Philadelphia.
What was discussed?
After Shays' Rebellion, which involved farmers rebelling against the taxes and closing down courthouses, the government decided to revise the Articles of Confederation so something like that won't happen again
Which plan was chosen?
Why not both?
Fifty-five delegates from twelve states attended the convention, with Rhode Island deciding to boycott it. Benjamin Franklin was the oldest to attend at 81, while the average age of the delegates was 42. James Madison was considered The Father of the Constitution and George Washington was president of it.
A variety of ideas got discussed here, a main one being the rule of secrecy. Two plans were discussed, the Virginia plan and the New Jersey plan. The Virginia plan favors the big states(populace) while the New Jersey plan favored the smaller states.