If I share a folder in Google Drive can they see my other folders

No, they can’t see any other folder. They can only see the folder that you have shared and the files inside that particular folder. But they can’t see any other folder in your Google Drive.

If you share a particular file with one email ID, only that guy can see that one. But if you share the file as a link, then anybody who has access to that link can access that particular file or folder.

Check out: Unable to change sharing settings Google Drive