You don't say what kind of essay you need to write, or how long it should be, but I will give you some suggestions as to what you could talk about and key points to cover.
This is an extremely short fable about a lion and a boar who come to a drinking hole at the same time, on a day when the heat has driven all the animals to try and seek out water. As such, when the lion and the boar, both symbolically strong animals, reach the water, they begin to fight with each other over which of them should get to drink. When they pause for breath, however, they see a group of vultures waiting in the distance and realize that the vultures have gathered in anticipation of either the lion or the boar being killed in the fight. Whichever is killed will be eaten by the vultures.
When they realize this, the lion and the boar decide to simply drink together as friends, because this is far preferable than either one of them becoming the vultures' food.
In your essay, you may wish to create a thesis based on what you think the moral of this story is. The moral is usually interpreted as something like: when two people fight, there is often someone waiting in the wings to take advantage of their defeat.
In writing your essay, then, you might consider how this story is applicable to the modern day. What is it really saying?
It is interesting that the two animals who are fighting are a lion and a boar. Both the lion and the boar are symbols of great strength, but the point of the story seems to be that if one great strength cancels out another, the one that remains will end up in a weakened position. Through fighting unnecessarily, it diminishes its own strength, allowing others to prey upon it.
You could argue as to who or what the vultures might represent. A vulture is a creature that waits until an animal is dead to feast upon its corpse; it does not get involved in fights itself, but simply waits until others have destroyed themselves. In the modern day, tabloid journalists are often referred to as "vultures," who wait for events to happen and then "prey" on the aftermath for their writing. The term "vulture" usually indicates that somebody is extremely unscrupulous and without morals. In adapting the context of this story, then, if we see the vultures as predatory journalists, who could the lion and the boar represent? They could be two high-level celebrities having a public argument, after which the vultures of the press will destroy the reputation of the losing one. Or we could interpret the lion and the boar as two great powers at war, with the vultures being a weaker country who waits until the fight has diminished the two big armies in order to creep in and claim victory, one country now being defeated and the other greatly weakened.
There are lots of essays you could write about this story, but because it is so brief, I think a good angle to take would be to summarize the story, explain the moral, and then argue that the moral is still applicable to us today. You could then identify several situations in which the story could be applicable, and explain what it would mean in those contexts. I hope the above suggestions give you a place to start.