Jewelry and other products made in gold and silver are marked according to their content of precious metal. The most common silver alloy (alloy is a mix of different metals) in jewelry making is ”925”, more commonly known as ”Sterling Silver”. It is marked with , which stands for 925/1000 silver (92.5%). The most common gold alloy is 18K which stands for 18/24 parts gold. It is marked either [18K] or  for 750/1000 parts gold (75%).
In most cases they are also ”hallmarked” with the brand specific stamp of the goldsmith responsible for the production of the product in question. Gold has to hallmarked by law in most countries.
The hallmark and the metal content stamps are your guide to know you are getting what you are paying for. Keep a lookout for the [PL] hallmark.