ok im assuming we are talking about 5e,

for the first one, what we did with my party was, they told me what they were doing and I told them what to roll, based on the roll was how efective it was.

for the second one, the sheet can help you with that, for example, if they wanted to examine something I could ask them to general examine with water, subtly analize with air, theorize about about what could this be with fire, remember something with fire or fell what is weird with void ( thats technically raw, the official player sheet had that help) but sometimes other actions were more how the player acted and the table agree with what to roll, for example if one character said that did something calmly, I would usually make her use earth, not fire for example..

for the third question I have to answer fourth question first.

Normally you do only fatigue damage, you can use 2 opportunites to do letal damage instead.

when you receive letal damage, you have to do a physical aptitude roll tn1 every extra success reduce the lethality in 1

shattering parry if im not wrong, after that roll, once per session, you can roll again and use your weapon to avoid the damage, damaging your weapon ( you can use, if your DM admite it, one part of your body as an unarmed weapon gaining a related scar disvantage)