I believe that is a species of Hygrophila, but that doesn't matter, as it is a stem plant and pretty much all stem plants respond the same way.
It will naturally grow toward the light, and the plant will put its energy into the growing end. This means the stems will grow longer and longer. Cutting them off just above one of the nodes will cause the stem to divide and grow two new stem shoots, at least this is the general reaction, I can't say if all species will do the same, but those I've had will. The "node" is the spot at which the leaves are attached, and on many stem plants leaves and roots may develop and grow from the node.
When you do this, you can then plant the tip portion that you cut off, and it will grow as a new stem itself.
Byron.