If we think about the great epics of the western canon, then we will probably think of the works of Homer and Virgil. There are many commonalities among the these works. Let me name a few.
First, they all have to do with travel to a certain extent. The Greeks go to Troy to fight and there are difficulties along the way. For example, Agamemnon (within the tradition) has to sacrifice his daughter to get favorable winds to arrive at Troy, and both the Odyssey and Aeneid are both very much about travel.
Second, all of these works are about warfare. There are many battle scenes. Men distinguish themselves in battle and winning promotes glory. This is seen in the similes as well as setting and plot. For example, in the Iliad, warriors are often compared to wild boars and lions. In fact, a common form is the work is "like a _____ when it _____."
Third, from a language point of view, all of these works are in dactylic hexameter. We can say that this is the meter of epic. These points should get you started.