Part of the photography triangle is ISO. ISO is International Standards Organisation and measures the sensitivity of the image sensor. The lower the number the less sensitive your camera is to light and the finer the grain. In bright light, a low ISO number (about 100 or 200) can be used to get a clean image at most apertures and shutter speeds. However, in dim light, you may need to increase the ISO number to capture the image you are after (as it will allow changes in the aperture and shutter speed). There is a cost of a high ISO though… the image will appear more grainy (which is the appearance of noise).
Noise is a random textured pattern that interferes with the image quality, and is commonly described as grain. The higher the ISO the more likely you are to see this noise. Noise is caused by an almost electrical interferences of the pixels on the sensor. How distracting the noise is, depends on your person taste, some images the noise can add a gritty quality (as seen in some urban photography). Its all about finding the balance between the components of the photography triangle to get the image you want.
By upping your ISO, you are able to capture faster shutter speeds and narrower apertures.
Try to keep the ISO as low as possible depending on the quality of light that you are dealing with
Be prepared that in low light situations where you would need to increase the ISO that there is going to be a risk noise/grain
Happy Snapping, CJeffers x