This command invokes the Select Texture box, which lists all memory resident textures.  Double-click a texture to choose it.  The texture is immediately applied to all the currently selected faces, or if no faces have been selected - the entire object.  The textures with a ‘.BMP’ suffix are those that have been loaded into memory from bitmap files.  The others are permanently resident textures.  You can load more textures into the program with the Load Texture File command.  Textures applied to faces stay with the faces during editing operations.