Differences between Leo and Saggitarius.

Simple answer: take other Fire Signs that also include Aries and Leo

Leo is fixed so they are stubborn in their ways and refuse to be swayed by things.

Sagittarius is mutable, so they are more flexible and adapt to the situation and people.

Leo is ruled by the Sun, that makes them very ego driven and self-centered. Think of the Roman God Apollo as an example of Leo energy. He loves himself a lot.

Sagittarius is ruled by Jupiter, who is carefree and expansive. Jupiter a lot more often went with the flow and took advantage of things as they came to him.

Other than that, they are much the same.

In general Roman Gods archetypes are good examples of astrological types as well. Take Diana (Artemis) for moon, the rest are what planets themselves are named for.