The is a nice description here: Prepare your data for offline use | ArcGIS for Developers
Help for ArcGIS Pro on this topic can be found here:Mobile map package—ArcGIS Pro | ArcGIS Desktop
Some blogs post are here: https://community.esri.com/groups/explorer-for-arcgis/blog/2018/01/22/make-an-offline-map-with-arcgi...
and a discussion that explains on what is included and is coming can be found here: https://community.esri.com/thread/198258-how-to-get-arcgis-online-basemaps-into-mmpk
1. You could use Esri's Tile Package Creator (https://marketplace.arcgis.com/listing.html?id=9c9ddae83e5549bb88a2c22e87a18ba1) to create a tile package from the World Imagery service.
2. Then load this tile package into a new basemap map (Insert/New Map/New Basemap).
3. From here follow steps as provided in one of Xander's links Prepare your data for offline use | ArcGIS for Developers .
Note that you will only be able to view this new MMPK (that can now include raster images) in Pro and the latest release of ArcGIS Runtime SDK version 100.2.