As you surely have heard over and over again, squats and deadlifts stand at the top of the mountain in terms of packing on lean muscle mass while also burning off fat fast.
The main reason for this is because you use a lot of different muscles to work together while moving extremely heavy weights you can't handle for other exercises.
With the most muscles performing the hardest work, you see the best gains and also stimulate the largest hormonal changes.
 Research has even shown that performing squats can help to build up your upper body, even though there is no upper body movement in the exercise! So regardless of your goals with working out, the squat, the deadlift and all of the variations between the two are the ideal exercise to perform.
 If you don't want to invest some of your time and energy in getting great results, then fine.
Spend your time doing hours of cardio and bicep curls.
If you're ready to really change your body though, it's time to use these excellent movements.
 You can perform squats really with any kind of weight, ranging from barbells to dumbbells to kettlebells or anything else.
The main ideal though is that you should always be using free weights, and never using any machines.
 This is because machines such as the Smith machine actually restrict your movement, not allowing you to maintain ideal ranges of motion and also taking away the use of the infinite amount of small, stabilizing muscles in use throughout your body.