As you can see it's not unlike the 4th. We just keep adding a new direction perpendicular to all the others and you got yourself a new dimension. It is not all that hard but figuring out where to put the other direction is very hard. We don't even know where the direction for the 4th dimension is yet, why think about the 5th? -
Because... we can measure higher-dimensional objects, we contemplate the meaning of the universe and so forth.
This window to the Fourth Dimension is hosted by the wonderful people at