Can someone explain Reives to me?

I've spent the better part of an hour reading and experimenting and I'm totally lost. I need to do some of these to advance in the RoV story line. I have figured out how get an assignment and add 1-3 currency. But I see I need key items to destroy obstacles? So do I need those each time, or only need to get them each 1 time? Also how do I know I'm going to the right Reive? Is it anyone that is on that map?

I'm getting way lost on this one.

the first KI you need is logging

https://www.bg-wiki.com/bg/Grind_to_Sawdust

but the full walkthrough is

https://www.bg-wiki.com/bg/Category:Reive

You only need the ki once and each area has a quest to do to get those ki. Any reive will count for credit.

KIs you only need once. Reives are otherwise a lot like FATEs in FFXIV, if you've done that.