Binoculars have two lenses usually either both biconvex or one biconvex and one biconcave. The length of the (binoculars or telescope) is the sum of focal lengths of the two lenses. The images appear inverted through the binocular. But for viewing a game or observing a distant object on Earth, we want to see upright images.
So we want to another lens in between the two lenses to make the image upright. The length of the telescope will be increased a lot (4 times the focal length of the inverting lens).
In order to overcome this, and the heaviness of the lenses and the lens holding tubes, we use prisms with small critical angles and high refractive indices. We introduce one prism to reflect (total internal reflection) rays from the objective lens. The rays are further reflected (total internal reflection) towards the eye piece. The prisms are kept a little tilted to the incoming rays. The shape of the path of the rays will be like a "Z".
In a binoculars, there are two objective lenses. There are four prisms. Then there are two eye piece lenses. There are more advantages in terms of weight, clarity, brightness of image, commercial advantage, compactness. The binoculars instead of being two parallel tubes, becomes bulged in the middle.