If you have placed all of your workers and you cannot play a card or do not wish to, then you must prepare for the next season. On your turn, bring back all of your deployed workers, then gain the listed bonuses for the next season, as shown atop the Ever Tree. After doing so, your turn is finished, and play continues with the next player.
Thematically the game begins in late winter and ends as the next winter approaches. Autumn is the last Prepare for Season action you may perform in the game.
Important: Players do not have to perform the Prepare for Season action at the same time.
Example: On your first turn, you place a worker on the 3 twig space and take the resources. On the following turn you place a worker on a Forest location to gain 1 twig, 1 resin, and 1 berry. On the next turn you play a Farm from your hand by paying the listed cost of 2 twigs and 1 resin; you immediately gain 1 berry from the Farm. On your next turn you play a Barge Toad from the Meadow by paying 2 berries, and then immediately gain 2 twigs from the Barge Toad because you have a Farm in your city.
On your next turn, you do not have enough resources to play any more cards, and all of your workers are deployed, so you prepare for the next season. You bring back your deployed workers, and then gain the bonus listed for spring: gaining one new worker from atop the Ever Tree, and activating all green Production cards in your city, which are your Farm and Barge Toad, immediately gaining you a berry and 2 twigs.