I bought the ukulele

So now, the question is: How do I tune this thing? Linda says that I need to learn at least 3 chords by the Kent State Folk Festival in Nov. (I plan on playing while I’m selling t-shirts and CDs). But, which chords? I don’t play anything other than piano, so this is all a little overwhelming (which, I realize is me being a little silly – I’m not planning on taking the stage at the Ark or anything). All help and advice is appreciated.