Sterling silver is an alloy containing metals that react with chemicals found in air and produce tarnish; a moisture levels, exposure of sunlight and contaminants such as salt water increase this reaction.
Take steps to protect your sterling silver by keeping it in airtight packages, use tarnish-resistant products (such as tarnish tabs or strips) that absorb harmful chemicals, and store metals in a cool dry place.
There are so many ways to clean them. Most tarnish is easily removed by polishing with a mild abrasive or soaking in an anti-tarnish product.
Please see my other pages for a few clearning options.