Ok this may be the dumbest question but

when people are saying for there wedding invites how to address the outer and inner envelope, what is the inner envelope for? so confusing

Apparently, as I have come to realize since I didn't use them, inner envelopes are supposed to clarify who exactly is invited. For example, if you just address the regular envelope 'Mr. & Mrs. So-and-So' but you're inviting all of your cousins who live with them, the inner envelope tells them this.

Yes, this has been a source of frustration for both my parents and the FILs. . .I've spent more time on the phone with them clarifying and RE-clarifying who gets a guest among my cousins. So, definitely use inner envelopes if you can!!!!

OMG i didnt even think of that im doing my invites sat so i still have time. Thank you so much

Here's a site that explains it. Your stationer should know, though.