A nautical league was 6,080 yards - or three nautical miles (each league being 6,080 feet). Note that there also US Leagues, UK Leagues and UK Nautical Leagues which all differ.
The metre is a unit of length in the metric system, and is the base unit of length in the International System of Units (SI).
As the base unit of length in the SI and other m.k.s. systems (based around metres, kilograms and seconds) the metre is used to help derive other units of measurement such as the newton, for force.