- The rulebook's guidance sets a minimum bound for combat rather than an average (my emphasis): "On average, a Company will experience
at least one combat encounter in one out of every two sessions of play". How much combat there is will depend on the situation and the plans PCs execute: sometimes they might charge in, sometimes they'll negotiate, sometimes they'll try stealth. And sometimes a situation will end up as combat even when the PCs were trying to negotiate or be stealth!
Combat can take place before a journey, during it, or after one. Chapter Eight "The World" has examples of various things that can lead to combat during a journey, the random tables included there give some great examples examples.
Good luck with your first game!