The Emancipation Proclamation was supposed to accomplish two goals:
1) Free slaves in the rebellious states (aka the Confederacy): This did not work, as the Confederate states felt that they were no longer part of the United States and did not have to follow the rules of the US government.
2) Allowed slaves to join the Union army- This move rejuvenated the Union army, as thousands of African-Americans that were currently slaves fled to the North in order to help the Union army. This would be critically in helping ensure that the Union had enough military forces to defeat the Confederacy.
