Can someone tell me exactly how this works?

Is it that a player will count as 1 season of pro ball if they are on the roster at game 25?  What if they are on the roster for a few days before then and then get sent back down to AAA?

Minor league assignments of less than 20 days are counted as major league service time.

Yeah, I don't really understand what you are saying tecwrg.

If the player spends the first 20 days of the season in the minor leagues, that will not count as major league service time.  That needs to be 20 days of the active minor league season, which usually starts one or two HBD days after the major league season starts.  If he does that, then he will not accumulate enough ML service time that first season to count as a full ML season, so you are getting one extra pre-arb season out of him.

If you call him up before 20 days have passed (let's say 16 days), then all those days will count as ML service time.  You won't get the extra pre-arb season out of him.  If you demote him back to AAA, then he'll have to stay down for at least 20 days to get the benefit of the extra year.

So if a guy plays on the ML roster for 50 games and then does a 23 game assignment in the minors and then is called back up for the remainder of the season then it will not count as ML service?  Am I understanding this correctly?

Correct.

Awesome!  Thanks!  I appreciate it!

So every single season a player(That has played at both the ML level and the minor league level) either burns an option year or has one year of ML service.  Correct?

Only if he has been added to the 40 man roster though at some time.

He had to be on the 40 to be on the ML roster.