Most actions will require a d8 to be rolled, and the result will be based on the roll. It's like a d6, except normal success, weak success and normal failures have double the chance of other outcomes, and overshot require 9+. 1 is critical fail, 2 and 3 are normal failures, 4 and 5 are weak success, 6 and 7 are normal success, 8 is great success, and 9+ are degrees of overshot, which don't have normal amounts of overshot penalty until 11+. [Stat] rolls get any bonuses/penalties from that stat, advantage (roll twice and pick higher result) if that stat is the doer's strength, and disadvantage (roll twice and pick the lower) if it is instead their weakness.
Anyway, there are 3 ways to open the door: using the right key, which is an auto-success in normal circumstances; breaking open the door, which requires a roll of strength and endurance (the latter for flavor unless either on a normal failure if the door is very hard or critical fail is rolled, in which case minor damage is taken[will work on health/damage when it is about to apply]); and picking open the door, which requires a lockpickl and a dexterity roll. Thankfully, Witch Doctors start with a Jagged Pin, which can be used as a lockpick, but counts weak successes as failures, and breaks on a Critical fail.. (breaking means it enters an unusable state, unless said otherwise)
Another note on breaking open the door; either 2 minor strength successes or 1 normal or above success is needed to break it successfully.
REMEMBER- The GM needs to confirm to these rules or adjust them first.