When people find coins, they do one of two things: place them in their collection or get the value of the coin and attempt to sell it to other collectors. Usually, getting the value of a coin is complicated. You have to factor in the year of the coin, how many scratches it has, if there are any errors (and if those errors happen to be rare), and any mint marks on the coin. When it comes to older coins, it gets even more complicated because bullion values, demand, rarity, and various design values start coming into play.
Keeping coins safe and in good condition is just as important as finding and/or buying them in the first place. Most of the time, coins aren't just a straight piece of a metal. They are nearly always a combination of multiple metals (the amount of metals like gold and silver can affect the overall value of the coin) and are composed a way that might be hard to maintain. For example, pennies aren't straight pieces of copper, nor are they straight pieces of a combination. Pennies starting from 1982 are actually a zinc core with a covering of copper. Meaning, if mix an acid that only corrodes zinc, you will be left with a shell of copper. This change was made because of the varying prices of zinc and copper.
As a metal detecting enthusiast myself, I know how difficult it is to find good locations to search in. Then after you find a good site you have to find the owner to ask permission to search the site. I'd like to help you identify some of these good sites. I have compiled a list; you can search in without permission most of the time.
Fairgrounds and picnic areas are excellent sites to search in with your favorite metal detector. These two places are favorite places where people of all ages come together and have fun. What else do you think they do? They all have money to spend right? Some of this money will be dropped and end up buried in the ground, the perfect scenario for us treasure hunters to take our metal detector and look for good finds.