Ok so board consists of 2-3 storys/bountys for each node that get you reputation upon completion. Accumulating this reputation is the currency you spend to play the reward challange nodes on the board.
(So the story/bounty missions are pre-requisite to playing the board.)
The key factor here is you can only do lets say 3 story/bountys daily to accumulate reputation ... and the nodes on the board are the reward you get access to for spending that reputation to unlock (largest reputation cost) and repeat daily (cost so you could repeat same node x3 per day for the node rewards i stated above) at increasing difficulty for each repeat. (This is where the player lv roster depth factors in) So only highly developed lv 85 players can hope to accumulate enough reputation to unlock a node (make that cost a whole days 3 story/bountys to unlock) and then repeat it subsequently.
That way at say lv 70 you should be able to do story/bountys for first node and unlock it. Then do it once , but its too hard to repeat on harder difficultys....this will allow you to accumulate reputation as you progress to lv cap so you can spend that reputation unlocking nodes once you think your strong enough. (Or lose it permanently if you fail).