All silver will tarnish over time. It is very easy to keep you silver jewellery looking clean and shiny though. Ideally you should store your silver in an airtight container away from the light (keep it in the grip seal bag that it came in). Give your silver jewellery a quick polish with a silver cloth before wearing or if it is beginning to look dull or tarnished. Heavily tarnished silver can be cleaned using a “Silver Dip”, which should be readily available from your local hardware or from larger supermarkets. Do not use a silver dip with silver jewellery, which has an oxidised finish or which has stones, ambers etc.
If you have a natural high acidity level in your skin, it is also possible that your finger may "turn green". That does not mean that there is a fault with the silver or the manufacture of the silver jewellery. For people with a higher acidity level sterling silver can cause your finger to stain. How your skin reacts with silver can also be affected by diet.