The conventional reel has a spool that rotates and may or may not have a device called a level wind that lays the line evenly across the spool as it is retrieved. The drag is adjusted by either a lever or a star knob on the end of the reel near the crank handle. There is generally a clutch of some sort that disengages the spool from the drive train. Almost all conventional reels have some sort of clicker that makes noise when you leave the reel in free spool and a fish picks up your offering. The conventional reel is somewhat difficult to fish with light lures and is also problematic when fishing into a strong headwind.
While it is more difficult to learn how to cast a conventional reel it does have several advantages over a spinning reel. The conventional reel can cast heavy offerings with heavy lines farther than spinning reels. They typically have more substantial drag systems than spinning reels and it is easier to drift your bait or lure in the current with a conventional reel. The decision to choose a reel with a level wind or not should be based on the type of fishing and type of line that you plan on using. If you plan on fishing with artificial lures or eels at night or you plan on fishing with braided line you will definitely want a level wind. If you plan on still fishing or fishing with monofilament line you may find that a reel without a level wind gives you slightly more distance.