A little bit of mucus in your stools causes jelly like stools and is normal.
However if your stools are really Jelly like and doesn't go away then your stools are containing too much mucus and is likely caused by an infection of the intestines which should be checked out by your doctor.
Intestinal Infections such as s salmonella, gastroenteritis, and shigella can cause Jelly like and Stringy like stools so a doctors visit is recommended because if it happens more than once or doesn't go away then something is wrong.