Does somebody knows when it´s ummer and when it´s winter?

jevaz said:

If I remember correctly, the Starks have this saying... "winter is coming." But if winter is always coming, I suppose then that it is never actually winter? So to answer your question, I guess the Starks don't know when it's summer or winter, and they're of no help at all in determining the current season.

(by the way, see Black Raven and White Raven in the first two chapter packs of A Time of Ravens).

Said more plainly...

It is Summer only when a card effect is in play that makes it Summer (i.e., the card says "It is Summer"). Currently, the only card in the game (right now) that does this is the attachment card "Black Raven" from the "Song of Summer" Chapter Pack.

Similarly, it is only Winter when a card effect is in play that makes it Winter (by saying "It is Winter"). The only card in the game that does so (right now) is the attachment card "White Raven" from the "Winds of Winter" Chapter Pack.

In general, this is a very card effect-driven game. If something is "missing" from the Rule Book that explains when it is Summer or Winter, or what it means to have the Ally trait, or something like that, it is usually because there is an effect on a card somewhere that creates the situation.