Well, you can find a one page summary of the entire play here: http://www.enotes.com/midsummer/35114
If you want a more detailed summary, please see the Summary and Analysis section of the enotes study guide on the play.
If you want the play summed up in a nutshell, it is this:
Two young couples who are having difficulties in love flee to the woods near the city. That same night, a group of workmen go to the woods to rehearse their play for the upcoming marriage of Theseus (ruler of the city) and Hippolyta.
There are fairies living in the woods, and the fairies play magical tricks on the lovers and working men for their own entertainment (and because there is strife among the fairies). The next morning, the magic has worn off, and everything works out. The lovers get together and are happy, and the workers perform at the marriage celebration.