One of the main differences between drama and fiction is that drama normally lacks a narrator. In other words, Shakespeare does not actually use exposition to describe Helena, or any of the other characters in the play. Instead, we learn about them through dialogue. We gain information about Helena from her own words and actions and the ways in which she interacts with and is discussed by other characters.
Both Hermia and Helena are typical ingénues, young rather innocent females in love. Unfortunately, both Lysander, and Demetrius love Hermia. The first time we encounter Helena (Act I Scene 1) she appears jealous that her ex-boyfriend Demetrius is now courting Hermia. Helena's plea to Demetrius that he let her be near him even if it involves mistreating her indicates some lack of self-respect or dignity:
I am your spaniel; and, Demetrius,
The more you beat me, I will fawn on you:
Use me but as your spaniel, spurn me, strike me, ... (Act II, Scene 1)
In Act III Scene 2, we discover that Hermia is short and Helena tall, and that they were close childhood friends, and we have a rather entertaining quarrel in the aftermath of Puck's mistake. The final plot resolution is worked out mainly by the male leads, and does not really add to our understanding of Helena.
Shakespeare paints, in Helena, a portrait of someone so in love with her rejecting ex-lover, Demetrius, that nothing else matters to her... not her safety, not her self-respect, not her sense of loyalty to her childhood friend, Hermia. She is depicted as so extreme in this obsession that what would be hard to watch, e.g. her willing acceptance of Demetrius' abuse, becomes highly comic. The Lovers are, in many ways, interchangeable, in that they represent different aspects of youthful, romantic, passionate, unthinking behavior. Helena, like the other three, is tossed and tumbled around in the fairy-ruled forest like ingredients in a mix, very like the youthful experience of romantic love, which, by the way, was a popular concept in Shakespeare's work. Our present day concept of Romantic Love has come to us in part from William Shakespeare.
Helena represents blind, romantic obsession. It is humorous because of her innocence and because of its utter dominance of her character.