hello !
well. with the power lever you set the power output- so make sure you do not exeed torque, gas generator speed and ITT limits. on takeoff you are typically torque limited, at altitude gas genartor speed or ITT- but not sure if fsx simulates this correctly.
with the prop lever you set a target prop rpm which (inflight) is held constatly regardless of the power output . typically full forward on take and landing and lover values for climb and cruise- the exact numbers differ between models.
with the condition lever you start introducing fuel into the engine at startup and also shut off the engine . some models have just a stop-run position, some have low idle and high idle. so here you can also set the idle speed of the turbine. typically you always are nearly always in low idle.
have fun !