"Ma soeur va se marier au printemps." it's something that people would say but should not write. It's like a word to word translation from english "will marry", in oral, people use future tense of verb going ("va") to translate "will". " Je vais manger. Tu vas danser. Il va se marier. Vous allez voir." But correct French would be : " Je mangerai. Tu danseras. Il se mariera. Vous verrez." Donc à l'écrit, il serait mieux de dire : "Ma soeur se mariera au printemps."

"va" is the verb "to go" in the sentence "ma soeur va se marier au printemps" I think the translation is "My sister will be married on the next spring"

"va" est le verbe aller au présent (au futur c'est "elle ira")

"va" est le futur du verbe "aller"