First of all a gold-piece is an object most people will never see in all their earthly existence. Contrary to what most writers of role-playing systems seem to believe only very few historic countries on a Dark Age or Medieval level of technology ever minted gold coins in sizeable quantities. Most currencies relied on a silver-standard. That means that the unit of measurement of which all coins are only fractions of was a weight in silver, not in gold. Throughout the European Middle Ages there was only one country that kept up the gold standard: The fabulously rich Byzantine Empire. Its gold-coin -the famous "bezant"- was the only gold coin of the Christian world for almost half a millennium. Later it was imitated by its main competitors in the Mediterranean trade: Genoa and Venice, later Florence the commercial and banking centers of the late Middle Ages. Gold coinage was restricted to a few areas of extreme economic preeminence throughout all the following Age of Chivalry - Northern Italy, Flanders and Byzantium.

In the late 13th century many of the nascent European national monarchies - France, England, Castille (Spain) and Norman Sicily tried the change to a gold-based coinage. All attempts were abandoned after only a few years. Only when the Spanish tapped the riches of a whole continent in the 16th century did they start to strike the famous gold-coin of the swashbuckling era: the doubloon. Never the less the standard Spanish currency unit of the era remained the peso, which was a silver coin.
Gold coins were prestige money and trade money for most of the pre-industrial era. So, to keep it simple, have your characters encounter gold coins in transactions where you are likely to encounter 500 Euro bills in a modern setting. Gold coins were for the use of a privileged minority only. This is one reason why they remained rather pure and reliable. If a state had fiscal problems it would simply stop minting gold coins instead of issuing debased ones. Even coins have a reputation to uphold and damaging it by debasing them is a really bad idea.

On the other end of the spectrum, copper coins were not common in the pre-modern economy. During the whole era after the collapse of the Roman Empire any copper coins you may have encountered were very debased silver ones. The smallest silver coins were indeed very small and transactions on a level below the scope of silver coinage were usually made via barter or did not happen at all. Simply forget about copper coins in a Dark Age to Renaissance setting. Most societies simply did not have a demand for small change. Copper coins will only surface in a setting imitating the Ancient World or in a Late Colonial or Industrial context. There they replace the smallest silver coins of the other eras.

Silver coins are the everyday money, the stuff that greases the wheels of the intricate machinery of economy.