It's a sort of psuedo europe: no wyverns/ogres etc., but place names have been changed, basically you are the monarch/ commander in chief of a kingdom, and you can engage in/avoid conflict depending on your answers to RPG style dialogue. In battle, you can either let the battle play out (blindly), or be on the battlefield with them, leading the charge (including standing back and watching if you wish). You can manage (hire/fire/equip) the fighters in your horde, and can tell them to charge.
Just been having a quick look for some more info for you, and noticed they've announced a sequel (release TBA) called 'Mount and Blade: Bannerlord'....which you may wish to wait for!
also noticed on the wiki, that you can download the full game, and play up to level 7 without a key, as a try-before-you-buy!
link to DL here:
https://www.taleworlds.com/en/Games/Warband/Download