Three witches (a.k.a. the "weird sisters") meet on a foggy heath (an open plain) in Scotland, amidst thunder and lightening. It's all very dramatic and mysterious.
They discuss when they'll meet again, and decide to hook up "When the hurly-burly's done, when the battle's lost and won." The implication is that they've been up to something really naughty. Brain snack: Even though the play's speech headings and stage directions refer to these three lovely ladies as "witches," the term "witch" only shows up once in the play.
The sisters are, however, called "weird" six times, but not "weird" like kooky and strange; they're "weird" like "wyrd," an Old English term meaning "fate." Spooky.
They let the audience in on their plan to meet some dude named Macbeth. Title alert! The witches then call out to Graymalkin and Paddock, the witches' "familiars," or spirits (usually animals like cats) that serve the witches.
All three witches then chance, "Fair is foul and foul is fair" before going back about their supernatural business.
Want to see how it all goes down? Check out this video version, from the folks at This is Macbeth.