Each of your Merry Men has a unique set of abilities, which make him more or less appropriate for a particular mission. One you get to know the members of your party well, it will be far easier for you to decide which of them you want to include in the team for a certain mission. Robin, for instance, has the ability to distract enemy soldiers by throwing gold-pouches, Will Scarlet can strangle enemy soldiers silently, and Little John has enough strength to remove dead and unconscious bodies from the scene of the crime.
The third, or should I say the first real mission, will start in the Sherwood Forest which is something like your headquarters in the game. It is here that you will choose your assignments, form teams and start missions. The missions are versatile and each mission has a set of minor goals which can be anything from robbing passengers to besieging an enemy castle.
Whichever mission you play, and whatever goals it may have, your success will depend on carefully planning your moves and staying out of enemy's sight. If the enemy does spot you, their excellent AI will take over, trying to alarm the head of the watch, or summon reinforcements, or even attack you if it assesses it is in a batter position than you. This is when the fight starts, and you better have click-happy fingers if you intend to win (not even this helps if you are severely outnumbered). The enemy troops will also be alert if they find a dead or unconscious body. Still, the most irritating of all are the stupid peasants (who you practically work for in the first place) that tend to reveal your positions to the enemy every chance they get. Enemy soldiers have a defined sight range that you can check like in Commandos.