I think you can transfer two players between 'matchdays' (as in one whole round of fixtures) - if you don't use your transfers then only one can be carried over.
I hope I have that correct.
As far as subs go, you can sub four players a day but no one on the bench at the end of a 'matchday' (round of fixtures) accrues any points.
Sub out a maximum of 4 players (unless they've been sent off), and replace them with any of your subs whose teams are yet to play within the matchday. Any players you sub out will score 0 points for that matchday.
ETA: Sorry, this was supposed to be a reply to @Gordopolis