The Yo-Yo is a variation of Fake Columns in which
the "faked" ball is moved on top of the center ball, as if they were
attached by a string (hence the name). Like Fake Columns, the Yo-Yo is a
favorite among younger audiences, and is in fact very easy to juggle.
The only tricky part of the Yo-Yo is the vertical carry, since you must make sure that the space between the two balls stays roughly the same, or else the effect will be severely diminished. Therefore, you should start with two balls, and practice just the fake.
Once you have that part down, you can begin to incorporate the Yo-Yo into your normal Columns pattern, starting with just one or two in a row and working your way up to doing the trick constantly.