From Mayoclinc website
Seperated Shoulder
separated shoulder is an injury to a part of one of your body's most mobile joints — the joint formed where the top of your shoulder blade meets the end of your collarbone. A separated shoulder is a stretch or tear of one or more of the ligaments supporting this joint.
A separated shoulder doesn't usually require surgery. Conservative treatment, such as rest, ice and pain relievers, is often enough to relieve the pain of a separated shoulder. Most people regain full shoulder function within a few weeks after experiencing a separated shoulder.
Dislocated Shoulder
A dislocated shoulder is an injury in which your upper arm bone pops out of the cup-shaped socket that's part of your shoulder blade. A dislocated shoulder is a more extensive injury than a separated shoulder, which involves damage to ligaments of the joint where the top of your shoulder blade meets the end of your collarbone.
If you suspect a dislocated shoulder, seek prompt medical attention. Most people regain full shoulder function within a few weeks after experiencing a dislocated shoulder. However, once you've had a dislocated shoulder your joint may become unstable and be prone to repeat dislocations.