Jewelers and coin dealers usually buy gold and silver.
The metal used for low value coins is typically copper or a combination of copper and other metals like zinc.
With the exception of a few very noticeable errors such as broadstruck coins, 99.9999% of bent coins are the result of damage. That makes them worth only their face value or metal value, whichever is higher.
Many years ago coins contained their value in metal. That is, a 1 dollar, 1 franc, 1 ruble, etc. coin contained one dollar, franc, or ruble's worth of metal. Copper is an abundant and readily-worked metal so it was used for low-value coins. Medium-value coins were made of silver, usually with a bit of copper mixed in to make the coins more wear-resistant. Finally, high-value coins were made of gold. The relative values of each metal allowed coins to be made in convenient sizes while containing their worth of each metal. For many reasons - economic growth that outstripped metal supplies, inflation, political interference, and other things - it became more and more difficult to use precious metals in coins. In many countries, including the US, the metal in coins became worth more than the coins themselves which led to people melting coins. For example at one point in the 1960s it was possible to melt $10 worth of US quarters and sell the metal for $300 to $400. Starting in the 1920s and extending into the 1970s most countries stopped minting coins out of precious metals. Copper remained inexpensive so low-value coins continued to be made from that metal, while nickel replaced silver in medium-value coins. Nickel has characteristics that make it useful for coins: it's abundant, has a color that resembles silver, and is very wear-resistant. Other metals such as, brass, zinc, and steel have also come into common use in coins. Many countries now issue brass coins because like nickel it holds up well in circulation and its golden color is easily distinguished from nickel and copper coins. Steel and zinc have come into use as a replacement for copper in very low-value coins because even copper is now too expensive for small coins. Both metals react to oxygen, however, so steel and zinc coins are normally plated or coated with another metal to prevent oxidation.
Before you sell, get as many opinions as you can as to grade and value of the coins especially if you have little or no experience, a coin show is a good place to start. I strongly suggest doing some research on the coins you have. Get a copy of "Red Book" it's a guide book for US coins, this will give you a basic idea of grade & value of your coins.
They re-sell them (they only pay you a fraction of the value.)
The value of obsolete currency and coins depends on several factors. If you mean coins, they sometimes have a metal content that has value, if they are silver or copper. This is "melt value", for the intrinsic worth of their metal content. These items may also have collectible, numismatic value. The price they might bring would depend on their condition, and their scarcity. The market for such items can be thin, and, in the end, the value of such items is what somebody has just paid for them. Some Nazi German coins of silver always sell, but they also made some of zinc that get this white residue all over them and they do not sell, unless perfectly preserved.You could always try listing them on eBay. Good pictures or scans help sell there. Unless the items you have are in perfect, pristine condition, they are unlikely to be worth any significant sum.
At the present time, the US has silver colored coins made out of nickel, alloys of copper and nickel, and other metals, but it no longer uses actual silver, which is very expensive. Historically, when coins were first introduced in earlier civilizations, and even in the earlier years of US history, the value of a coin was the value of the metal of which it was made. Silver coins were valuable because they were made of silver, a precious metal, gold coins were even more valuable, and copper coins were less valuable because copper is a less expensive metal, although still expensive enough that coins made out of copper have value because of their metal content. Now the value of US coins is like the value of US paper currency, something that the government declares, rather than being the result of valuable metal content. But out of tradition, the higher denominations are still silver at least in color, and pennies are still copper.
The value of coins comes from how old they are, the condition, and the metal they are made from. Some older coins have different faces because the leaders of countries change over time.
In US dollars it has a melt value of $1.37. It is illegal to melt these coins for the metal they contain.
Banks will happily buy gold coins for their face value - since this is nearly always far less than they are actually worth. If you wish to sell your coins for their actual value, take them to a reputable goldsmith.
No coins are not because they are metal and metal is a conductor.
One cent. It's not a US Mint product. In the years following JFK's death a lot of companies took ordinary cents and used metal punches to stamp his image on the coins, then sell them as "commemoratives". In reality they're considered to be altered coins and novelty items with no added value to a coin collector.