The announcement post notes that the beta “features online play and, as always, any career progress you make during the Beta will carry forward when the game updates upon full release [4 November].” There’s a caveat that any online games may not carry forward from beta to full version, but that single player games should be fine.
The Football Manager 2017 beta is available to anybody who has pre-purchased the game. People who pre-ordered on Steam should be able to get the beta downloading by launching the game from their Steam library. Those who purchased through other retailers should have received or be receiving their beta codes to input into Steam, today. See the forum thread linked above for more instructions if necessary.