The source ASE instance is normally your production ASE instance. It is the source of the data that you would like Delphix to start staying in sync with.
The staging ASE instance holds all of the data that Delphix copies from the source database on Delphix storage.
The way Delphix stays in sync with the source database is that it monitors the source database's backup server log file. When it sees that there is a new database dump or transaction log dump created, it loads the dump into the staging database. If this is done successfully, you will see a timecard on your dSource reflecting the date/time of the dump.
After the data has been successfully ingested into the staging database and a timecard created on the dSource, you can select the timecard you want and provision a VDB from it.