Google how to shoot manual on a camera and practice practice practice until you can. At that point, you will know that you want your ISO as low as possible, preferrably between 200-800 at the highest. The higher the ISO number, the more noise you will see in your photos. Also take into account that your images will not be viewed at 100%, but instead at 1200 px wide at the most unless you are making prints larger than 15". If noise is not detectable at that size, you're good to go. However, always try to keep your iso as low as possible, and your shutter high enough that you don't get blur and "unsharp" images.
Professional photographer for the past 12 years.