How match money my coin worth

One of the first thoughts of a person to whom accidentally got a coin - what is the price of this coin and is it possible to get money for it? Maybe you can. But in order to find out, you have to work a little.
Supposedly you know what coin you have, you need to know what the value of this coin. There are coin catalogs, both paper and electronically translated, but prices in them almost always do not correspond to reality. This is understandable - the price of a coin depend on many factors, so also the catalogs were published some time ago (and sometimes very long ago) and the prices most likely changed significantly. So, numismatic catalogs serve more to identify coins, and not to determine their value.
The easiest way to evaluate a regular (not super-expensive) coin is by comparing prices at online auctions, such as Ebay.

At online auctions there are two options for placing goods on sale - "buy now" and classic auction. The second sale option may not be much different from the first, if the seller puts the initial value close to the desired sale price. Therefore, if somebody can to sell a coin at a certain price, this does not mean that at this price someone will buy it. In practice, the more or less real value of the coin can be determined by subtracting about 20% of the minimum fixed price found (or the price if there are no bets).
It may turn out that the coin is sold with a start from a low price (perhaps even from $1, if it is obviously in demand) - in this case, the result of the sale will show the real value of the coin. You just need to wait for the end of the auction.

Of course, it may happen that there is no such coin at the auction. Then you need to try to expand the search area, for example, do not write the year - only the country and denomination, and then select the type of coin.
Further so - if the coin is cheap, then with a clear conscience you can keep it as a souvenir, or give it to a child. If expensive (and, especially, very expensive) - no, do not run to sell it, but make sure that the coin is genuine.
Well, if information about a coin or its value could not be found, you need to ask knowledgeable people. Naturally, you will need a photo or scan of a coin - no one will determine according to the verbal description. You can try it - reddit.com/r/coins/
Of course, what they write about the coin is not the ultimate truth, but information for reflection will be added.
You can, of course, start with this item (numismatic forum). Many do so, rewarded with an unflattering assessment of local inhabitants, in case the coin is simple and yielded to an independent definition. I still recommend first to search for yourself - very often, it is easier, faster and more pleasant.