To build greater strength you’ll need resistance, and this resistance comes in many forms, most in which you’ll be working against gravity (a downward force).
Indeed you have:
Your own body weight. Kind of self-explanatory, you get into lots of different positions and move your own body weight.
Free weights. You lift an external weight. Weights come in many forms, from the barbell and weight plates, to dumbbells, to kettlebells, and everything in between. Each type of weight training implement has it’s own unique advantages and disadvantages.
Machines (fixed weights). Most machines use adjustable weight stacks, pulleys, and cables to manipulate gravity and provide resistance.
Bands. The actual band material provides the resistance. The resistance is adjusted by using heavier and thicker bands. This is a common form of resistance that doesn’t use the downward force of gravity.
So what type of resistance should you use?
For strength purposes, most of your training should be with free weights.
Free weights allow you to adhere to the principles of strength training, they’re cost-effective, and they’re functional.
Body weight training should also be included. Manipulating your body weight is incredibly important, and it can help you learn kinesthetic awareness and bodily control. Body weight movements are also great for conditioning.
Machines and bands should be used sparingly if you’re not rehabilitating an injury.