This page provides some basic information on unit types in Mount&Blade: Napoleonic Wars. Use the menu to go to the desired section. More detailed information is disclosed in the movies :)
There are a few variations of infantry classes within Mount&Blade: Napoleonic Wars, such as partisans, line infantry, light infantry, guardsmen and riflemen. Classes are referred to by their actual regiment name but immediate differences in weapon loadouts can be recognized. For example, riflemen tend to have more accurate firearms but no bayonets while line infantry is generally not equipped with swords (varies depending historical regiment). Each class has subtle variations in stats that are intended to reflect their advantages without disrupting gameplay balance.
There are a few different types of cavalry which are categorized as light, medium or heavy cavalry. This is intended to reflect the manoeuvrability or speed of the selected cavalry regiment. Cavalry classes vary from dragoons, lancers to light or heavy cavalry, each with both their own advantages and disadvantages.
Beside the infantry and cavalry, the game offers a range of specialty classes to aid the troops with cannon, fortification, and leadership. The specialty classes take some getting-used-to, but are invaluable during the course of the game.
A breakdown of the rank-system in Mount&Blade: Napoleonic Wars can be found here.
More / extra info
Some last-minute information I discovered.
Countries and their regiments
A detailled set of Excel sheets with information about the various regiments in the game.