The New Tetris is one of the many, many versions of Tetris to have been released that just barely tweaks the basic formula. This one introduces the concept of Squares.

As you're playing this game, you're going to want to create 4x4 squares of blocks. You can do this by using different pieces, which will yield a silver Multisquare

Or you can do it with all of the same shape piece, which will yield a gold Monosquare

Now, why would you want to do such a thing?

Every line that you clear that includes one of these squares will give you Bonus Lines. And since Lines is the only way to keep track of what your score is, that becomes fairly important fairly quickly to get one of those really high scores.