well said Cherry. just an additional input, you will also notice someday the term 'right here', a bit the same with 'in here' in essence. "where are you the whole night? I'm just right here, waiting for someone to call me!" :)

Hello Camille, The word "here" demonstrates and points the location of something or someone in the vicinity * that is nearby*. Using "in here" is more specific , for it indicates that the object or the person is inside or within a certain space in the vicinity as well. If someone asks : "Where is the book?" "It is here on the table" (Pointing to the nearby location on the table) "It is in here " ( Pointing to its location inside another space ,could be in a bag or a box for example that could be on the table as well ). In fact you can hear both words used frequently.Maybe in spoken English specially among non native speakers they just point to anything saying "here" even if it is more precisely to use "in here". That explains why you wouldn't hear it spoken much at school. But when you read the written English the accurate expression for the location is used; hence you will find both "here" and "in here" applied adequately when reading them in articles.