The Missouri Compromise stated the following:
1) Missouri would enter the Union as a slave state.
2) Maine would enter the Union as a free state.
3) The 36'30 parallel would determine whether or not new territories added by the US would be free or slave.
This compromise was a result of sectional tensions between Northern and Southern politicians. At this time, there was much debate about whether or not slavery would exist in the new territories gained by the US through deals like the Louisiana Purchase. This was extremely important to both groups of politicians, as this could have huge implications on Congress. To settle this dispute, Henry Clay helped to create the Missouri Compromise in order to keep a balance of free and slave states in Congress as well as giving a "solution" to whether or not slavery will exist in new territories gained by the US.