Summary:
In any gym, you are going to find that the main features are two things: weights and weight machines.
In any gym, you are going to find that the main features are two things: weights and weight machines. This is because weight training is such an important part of going to the gym: it is one of the most energy-burning kinds of exercise you can do, and it builds strength and muscle. If you go to the gym and don't lift any weights, then you might as well have not gone at all.
The simplest way to weight train is to simply get the weights and lift them up, crouching down, picking up the weight, and then trying to lean back and unbend your knees to get back to a starting position. While this is simple, you can keep on making it more difficult forever simply by adding more weights to your pole - it is not difficult to make a weight that even the world's strongest man couldn't lift.
However, this kind of exercise tends to only exercise the same few muscles of your body over and over again. To make sure that you build muscles and get stronger all over, it is better to use weight machines.
Weight machines work in all sorts of different ways, but generally use either fluid or springs to create the illusion of weight, and then a system of wheels and pulleys to bring that weight to you. These materials create resistance without necessarily needing large weights, so you can set the difficulty of using the machine to artificially create weight level you want.
Each different weight machine is designed to train a different set of muscles in your body, which means that doing them all in a circuit will give you an all-over workout. Even if you find one machine particularly difficult, you shouldn't leave it out, as doing this will create a weak point in your muscles that could be dangerous for you.