Start where you are with your current fitness level and build your endurance and strength slowly. The early stages of getting fit requires that you learn the exercises. This is especially important if you have some old injuries that may need special modifications before you can increase your workout intensity.
One of the best things you can do after you learn the exrcises is to challenge your muscuar conditioning by combining exercises to do super, tri, monster and giant sets. Why do just one set of an exercise when you can do two, three, four or even five.
In the video above my client was advised to get shoulder surgery. He also had knee surgery years ago. When he first started exercising he was about 40 pounds heavier, got winded quickly and had to use machine exclusively. The exercises he demonstrates requires shoulder strength and stability. His knees support him without any difficulty when performing a free form back exercise and a cable chest exercises in a lunge position.
His doctors would be amazed!