This question comes in three parts. First, is your camera really as bad at high ISOs as you think? Second, is noise REALLY that intolerable? And is your attitude to noise stopping you from taking shots you might actually like?
This setting increases the camera sensor’s sensitivity to light. Each ISO step doubles the sensitivity, so it’s easy to use ISO as another exposure control alongside shutter speed and lens aperture. Increasing the ISO increase noise, however.
Noise is the digital equivalent of grain in film. It’s random electrical signals captured by the photosites on the camera sensor, and usually this background noise level is so low compared to the brightness of the captured picture itself that you just don’t notice it.