Questions & Answers about Po drodze kupię chleb i mleko.
It means on the way or along the way.
So Po drodze kupię chleb i mleko means something like:
- I’ll buy bread and milk on the way
- I’ll pick up bread and milk on the way
It usually suggests that the speaker is going somewhere, and during that trip they will stop and buy these things.
Kupię is the future tense of kupić, which is a perfective verb.
- kupić = to buy in the sense of completing the purchase
- kupię = I will buy
By contrast, kupuję means I am buying or I buy.
So:
- kupuję chleb = I’m buying bread / I buy bread
- kupię chleb = I’ll buy bread
In this sentence, the speaker is talking about a future, completed action, so kupię is the natural choice.