A lion is a large animal similar to a cat. They are one of the most dominant animals in the wild and you can find them often in Africa. They have large mains and are preditors. Basically, if you are a Lion, you are in charge.

A lioness is a female lion. They do not have as much hair as the male lion. They take care of the young and even though they are females, they have a strong influence of their societies.

The similarities between the two is that they are both from the same species. They eat the same food, the both reproduce, they both hunt, they both are intimidating.
The differences are, the gender of the lions, the behavior and how they act towards other lions is different, the hunting and gathering of food. The core differences would be their behaviors and their gender.