ISO settings are the measurement of how sensitive your digital camera's sensor is to light. The speed or light-sensitivity of a digital camera's sensor is rated in ISO numbers -- the lower the number, the slower the response to light.
Generally, we get the best picture quality by using the lowest ISO setting (such as 100 or 200). Higher ISO settings, such as 800, enable us to shoot in lower light situations with faster shutter speeds..
Higher ISO setting numbers indicate a higher sensitivity to light, so less time is needed to expose a picture. Most digital cameras let us control the ISO setting to allow the use of higher shutter speeds and/or smaller apertures, according to circumstances
Memory cards are so inexpensive today, that it’s worth having an extra one so that you can get out and shoot as much as you can in as many different circumstances. Don't be afraid to try different exposure settings and use the different settings available on your specific camera model. The more you experiment taking lots of different photos, the more comfortable you will get understanding your camera and what works for the types of pictures you want to take.
Check your manufacturer’s website for their video tutorial and also check YouTube for more help learning to use your specific camera model.