To start with - most recent European coins are worth very little and are now being sold by the pound. Google "euro coinage" to discover which countries are using euro coins; these countries' coins before 1999 were mostly exchanged for new euros and many of the old coins sent to China, especially those containing nickel, for melting and recycling. However, most English decimal coins are worth at least face value. Most foreign coins' value now is mostly in filling out collections of type or date coins. Most Mexican coins before 1992 (when reform coinage went into effect) are worth bulk value, although there are some varieties that are worth a bit more. You can also check a money rate site online to discover what the current values of euros and Mexican reform coinage and other countries' coins are.
Earlier coins may be worth a premium, IF you do NOT clean them, and your best source of value information is the "
Red Book" or "Coin Values", which you can find on most newsstands. Even some recent USA cents may be worth substantially more than face value if they are "varieties" or "error" coins; you'll find very useful discussions of them in the error and variety forums here.
Welcome! Ask away with your questions - photos are very useful (no camera necessary; just scan them!) - be sure to include full information on any coins you need more information on, including country of origin, size in millimeters, weight (if possible), and any "odd" features that don't seem to match with type photos of your own coins. Hope to see you back here again.