Mike,
That's some question. Could you maybe clarify a bit what it is that you are confused with.
And here's a good place to start:
http://www.cactusumpires.com/
On this site, go through the powerpoint on lineup card management - at the end is a section on the DP/Flex.
Meanwhile, both Dakota & I put together some stuff that's pretty good too. You can look at that stuff on Joel Blue's site at eteamz. Here's that site:
http://www.eteamz.com/sites/GCBUmpire/
You find the stuff in his "downloads" section, I think.
Finally, since you're asking for Fed, I am going to assume that you've done Fed ball for a few years. There are only a few differences between today's DP/Flex and the old DH rules. Those differences are:
1-The role of the DH/DP is never terminated.
2-A team may go from 10 to nine players and back to 10 players any number of times during the game.
3-The offensive player and the defensive player for whom she is batting can play defense at the same time.
Let me suggest that you look at the cactus site, see the stuff at Joel's site, keep these listed differences in mind and then try to list what it is that is confusing.