Your main character drives the plot of your story forward through the outer motivation (the tangible goal of the character, like winning a boxing match, or recovering the fabled lost crystal skull). Internally, however, there might be a reason that is moving them forward, such as love or revenge.
At the same time, there are things that are keeping your character from getting to the finish line. The outer conflicts are the things the audience can see that keep them from completing their goal (Nazis, booby traps, a lawsuit). However, there can also be inner conflicts that the audience cannot see that can also slow down your hero (the loss of a loved one, a sacred promise, fear, etc.).
Find out more in this installation of Bill’s Screenwriting Tips!