where is the default contruction?

I was following a youtube tutorial for the openstudio sketchup plug in and i found that him had a default construction window where he could change the entire walls model into the same thing, (like all the interiors walls into air walls), so i was asking where can i find it or if is there a new option to do that type of things); also i'm new on this website so i dont know what i'm doing ahah

Is this the YouTube video? That one dates back 13 years ago, and things have somewhat evolved since then. I don't believe one can add new materials and constructions with the OpenStudio SU Plugin itself, yet one can create and/or modify default constructions and default construction sets. Look up the OpenStudio Resources with the Inspector :

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Once selected (maybe altered), assign one or more where needed (e.g. at the building level, to individual spaces). To add new materials and constructions, I suggest you follow these suggestions.