1 – Key Principle
The d10 is used for virtually all dice rolls, this is to allow a greater range of possibilities in the game, and to allow it to be scaled up if need be if you want to d% for skirmish games.
Getting High is Good
The key principle is to score high.
The games mechanisms require you to get 10 or more on any dice roll (with a few exceptions).
So in most cases the mechanisms are designed so that you have a key stat (Discipline/Shooting/Combat/Initiative) to which you then roll a d10 and add the result and try and get over 10 in order to be successful say at passing a Discipline test, or to shoot someone and so on.
Of course, there are modifiers +/- that might inhibit your achieving a 10+ result…