I am not aware of any tutorials but covering a square cake is not that different from the round ones.
Lay the rolled out fondant on to the centre of the cake and gently smooth down each side, trying to avoid stretching it. Amazingly the fondant fits to the shape of the cake. Try to drape the fondant over, like wrapping a present, to ensure you have not got lots left when you come to do the last corner. If you find that you have too much fondant on a corner you can always cut it off and smooth over the join.
I nearly always use fondant and it is amazing what little imperfections you can hide so don't worry. 
Panda
Try this: http://atecousa.net//learn/
Oops!! Sorry, I didn't notice you were looking for a square cake tutorial. The trick to doing the square cake is doing the corners first -- smooth the top, then pull out at the corner smoothing with your fingers then do the sides. Finish as you would a round cake.
On square cakes you'll need to smooth the corners first and then the sides.
Jacqui
When doing a square cake always work from the corners inwards. This will help you creating a smooth cake. I like square cake more than round.
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