OpenStreetMap is a database of geospatial information. Levels/floors are modeled with attributes of geometry primitives in the data (the level tag to be concrete). How attributes are made available to applications depends completely on what framework you are using so can't be answered without further context. But very roughly you can determine from attributes on the building outline the min and max level that re present and then simply only display objects with the correct level tag, for more information see https://wiki.openstreetmap.org/wiki/Simple_Indoor_Tagging

OpenStreetMap is a database of geospatial information. Levels/floors are modeled with attributes of geometry primitives in the data (the level tag to be concrete). How attributes are made available to applications depends completely on what framework you are using so can't be answered without further context. But very roughly you can determine from attributes on the building outline min and max level that re present and then simply only display objects with the correct level tag, for more information see https://wiki.openstreetmap.org/wiki/Simple_Indoor_Tagging