Postgres has had stored functions for ages, but only added stored procedures in version 11. Historically, you'll see people calling stored functions in Postgres "stored procedures" as that's what other folks call them. It didn't matter because Postgres only had the one thing. For what's new in Postgres 11 stored procedures, here's a place to look:
The change you're referring to is that a stored procedure (but not a function) has the ability to manage its own transaction blocks.
I actually have no clue...I've only read about the new stored procedures. But if you're coming from Oracle, you're likely looking for PG 11 stored procedures, at least some of the time.