If you want to import a raster dataset into a geodatabase, see About importing raster datasets. This help topic covers loading and importing rasters, as well as loading rasters into an empty raster dataset.
If you are working with raster catalogs, refer to Creating raster catalogs in a geodatabase. This topic discusses raster catalogs in geodatabases and how to create them.
If you want to add data to a raster mosaic, see Adding raster data to a mosaic dataset.