What this coin looks like (obverse, reverse, mint mark location, special features, etc.): This variety is an 1811/10 Capped Bust Half Dollar and features an overdate error. An 1811 date was actually struck over an 1810 date which resulted in what looks like a dot or period in the middle of the date as depicted by the arrow in the example image above. The end result was a date that looked like 18.11 - the dot in the middle was not by design but is part of the underlying date!
Coin value chart: Typical coin prices, values and worth in USD based on grade/condition