after migration from windows pc to macbookair, the macbookair shows 6 different users corresponding to the number of times I migrated different folders. Looking at the macbook air, I can't find the folders I migrated in the original macbook air

Migration Assistant is designed to transfer User Accounts: Move your content to a new Mac - Apple Support. Although you can choose among broad categories of items to transfer, each time you use Migration Assistant, it will create a User Account. It seems that's what you did.

The right time to transfer information to a new Mac is when you initially take it out of the box, turn it on, select a language, choose a geographic location, and otherwise generally configure it for one or more Users. That's all you needed to do, after which you never need to run Migration Assistant again. Since it appears that you deferred that decision until after initially setting up the Mac, you need to log into the one User Account that contains all the information you needed (Documents, Pictures, Desktop etc), and remove the redundant Accounts. Refer to Delete a user or group on Mac - Apple Support.