"Kupuję bilet autobusowy."

Translation: I am buying a bus ticket.

[conor.raff]

autobusowy is an adjective here, coming after the noun strangely....

http://en.pons.com/translate?q=autobusowy&l=enpl&in=&lf=en&cid=&srt=null

[Vengir]

If the combination of an adjective and a noun forms some sort of a "fixed phrase" (like „bilet autobusowy” or „igrzyska olimpijskie”) then the adjective typically comes after the noun it describes.

[mihxal]

It's common for adjectives which describe some subset of objects and its features are constant like "autobusowy" here. It's "przystanek autobusowy" and not "przystanek tramwajowy". But both can be called "przystanek".

[ankbhatnagar]

In case anyone is wondering, przystanek means a stop.

[Jellei]

Yes. Well, a place where one stops, mostly a bus stop or a tram stop ;)

[Jussimr]

"I'm buying a ticket to the bus"?

[JerryMcCarthy99]

No; "to" doesn't apply here. You could use "for" as in "I'm buying a ticket for the bus" (and that is accepted here).