In Act I scene 2 of A Midsummer Night's Dream, the "rude mechanicals" meet. They are some of the working men of the town, and they are meeting to plan their production of a play (about Pyramus and Thisbe) for the wedding of Theseus and Hippolyta. They plan to meet in the woods to practice.

That's the action in a nutshell. That's the plot, in other words. However, a few other things happen as well, on the level of structure and style. The play opened with some potentially serious themes (the lovers plan to run away, for example). Scene 2 provides comic relief, and lets the reader/viewer know things will be fun. What's more, since both the lovers and the actors are going to the woods, we know things will intersect.
It also foreshadows the sort of comedy that will happen: the men might be foolish in general because of their lack of acting skill, but everything is raised to a higher level of silly because of Bottom's ego.

Greg