In which order this events should be resolved in the start of turn phase:

1. Deal with conditions e.g Poison

2. Class abilities e.g. Concentration of the bard class ("At the start of your turn, if both your song tokens are on different Class cards, you recover 1 damage and 1 fatigue.")

3. Hero abilities e.g. Ispher ("At the start of your turn, recover 2 damage.")

In which order this events should be resolved in the end of turn phase:

1. Lose all fatigue because of a rest action

2. Class abilities e.g. Song of Mending of the bard class (" At the end of your turn, each hero within 3 spaces of you recovers 1 daamge.")

So could a bard get his fatigue back because of a rest action, then Song of Mending occure and then the bard spend one recovered fatigue to trigger his concentration ability ("Exhaust this card when a hero within 3 spaces of you recovers 1 or more damage. That hero recovers 2 additional damage.")?

when multiple effects occurs at the same time, the active player choose the order of the effects

and it's not "lose fatigue because of a rest action" but "recover"

@rugal I guess, Toadie1981 is referring to fatigue tokens.

Rugal is right. The active player decides on the order of events with the same triggering condition.

On Concentration:
Cards cannot be exhausted out of the step 3.II. (Perform actions; see CRRG) without a specific triggering condition. In this case though, "when a hero within 3 spaces of you recovers 1 or more hearts" is a specific trigger. Concentration can be used in step 3 (End of turn) the way Toadie describes.

Thanks again

So the player can make each round a different decison e.g. :

1. The player has only one health left and could die if he rolls for poison first, so he decides to start with "Concentration". So he discards one damage token and will survive the poison test.

2. In a later round the player has no damage, so he makes the poison test first, fails and heals the damage immediately by "Concentration".

The same for the end of turn:

1. The player has fatigue token equal to his stamina to he decides to resolve the rest action first followed by the healing effect of "Song of Mending" and boost this healing by "Concentration".

2. In a later round the player has one more stamina than he has fatigue tokens so he resolves the healing effect of "Song of Mending" and boost this healing by "Concentration" first, so that he now has equal fatigue tokens to his stamina.
Now he resolves the rest action, so he has zero fatigue tokens left.

You got it.