Quick question on working mirrored

Sketchup noob here. Been watching videos searching can’t find a specific answer to this so here i am.

With that said how do i stay working in a mirrored state? I understand how to duplicate something transform it on itself, and mirror it, but how do i make it so as im tweaking things on one side, it’s mirroring it on the opposite side?

Best example is here: 페느아트스쿨 : Concept Art - Space Ship ( SketchUp Modeling ) - YouTube

Sorry in advance i know this is a painfully straightforward question, i was just having trouble knowing the right search terms. I used to know how to do this but it’s been many months since i touched sketchup.

Make the first half into a component (not just a group), then mirror that component for the other half. Go back and edit the component for one half and the changes should effect the other instance mirrored as it is.