I am currently using Rosetta Stone to study Russian along with Wiktionary to understand the case system and have got pretty far. However this sentence is tripping me up. I've just broke it down below and hope someone can correct me if I state anything wrong.
В прошлую среду он купил билеты на поезд
[В прошлую среду] I understand the в doesn't cause the prepositional case for days of the week, and the adjective "last" declines to the feminine accusative case to match the case of среда (also for some random reason accusative).
[он купил билеты] He bought tickets. купил being in the masculine past tense and билеты being in the plural accusative tense as it is the object that is being 'bought'
[на поезд] Now I understand he isn't buying tickets ON the train which would be the case of the prepositional case was used (поезде). but I'm slightly misunderstanding what is happening here. is it nominative or accusative? why isn't it genitive (tickets of the train). Can someone explain to me what case and why it is being used.
Again anything above could be wrong i'm just going from what I know, Thanks for your help.