There is no cost to enter. You must register separately for each round to gain points from them. You need not register for all rounds. Points gained in any round will be carried forward until the end of the pool. Registration for any particular round begins immediately after the previous round ends.
Registration ends when the next round begins.
There will be at least 48 hours in which to register, even if this overlaps with the start of the next round. A player's picks are final when registration ends. Picks for the next round may be changed at any time before the end of registration.