Machines or Free Weights
Exercises can typically be done 2 different ways... by using machines or by using free weights. Machines are... well... machines. Free weights usually refer to dumbbells and barbells.
While both can be effective, free weights are better for the purpose of increasing muscle and strength. Here's why...
Machines are designed in such a way that they do part of the work for you. They keep the weight stable. The machine puts everything in a constant stable position that allows you to only have to move the weight from point A to point B.
Free weights on the other hand are just that... free weights. They are weights that aren't being held in place by anything except, well, you.
Free weight exercises require you to not only move the weight from point A to point B, but to also keep the weight stable throughout the entire movement. Doing so requires the use of additional stabilizer muscles which would not be used had you done the exercise on a machine.