It’s simply known as S/4HANA and not SF and SAP Simple Logistics any longer. Since S/4 1610 basically the whole former ERP/ECC was transferred to S/4.
It depends on what you mean. From a business point of view, the differences in terms of functionality are not that huge, so you can just start by that. SAP ERP is simply a tool independent of the version and not the most important issue for a functional consultant.
If you are someone who is reading this answer and do not know what SAP SL is then here is a quick video for you:
The technical basis with the underlying HANA DB is a completely new architecture. There is an SAP ABAP for HANA (Interface to the HANA DB at least) that has a totally new approach to development (code push down) and the UI is with SAP FIORI focused on web technology.