A flintlock has a pan for powder on the side of the barrel, a percussion gun has a nipple that you put a small cap on, the hammer hits the cap and sends a spark through the nipple to fire the gun. An in-line usually has a bolt like a centerfire rifle has and the primer goes in the end of the barrel. It can also be a break-open style. It is hinged by the rear of the barrel and a lever is used to open the gun.
Ardesa guns are made in Spain and are imported by Traditions Performance Firearms. They are copies of American made guns, mostly from the 1800's.
Flintlock guns in very good to excellent condition are worth $250 to $300.
Percussion guns in very good to excellent condition are worth $325 to $375.
In-line guns are worth around $200.
The best way to sell your gun is to list it on AuctionArms.com or Gunbroker.com. On both sites you have complete control of the auction. You set the starting price, bid increments, reserve price if you want one, amount charged for shipping, type of payment accepted, etc. You can include up to 10 pictures with each auction. The buyer supplies you with an FFL of the dealer they want it shipped to and must go through a background check when they pick it up. The commission rate is around 1% which is extremely low. You receive payment before you ship the gun and the best part is no one comes to your house to look at it. I have very good luck using AuctionArms to sell guns and parts and have never had a problem with them.
I hope this helps you,