When a noun is the direct object — the thing you want, order, buy or drink — its ending changes. Feminine nouns ending in -a swap it for -ę; masculine things (not people or animals) and neuter nouns simply stay the same.
Examples
- Poproszę kawę.
- I'd like a coffee, please.
- Piję herbatę.
- I'm drinking tea.
- Zamawiam zupę i sok.
- I'm ordering soup and juice.
- Poproszę rachunek.
- The bill, please.
The mistake to avoid
Leaving the dictionary form after "poproszę" — it's "poproszę kawę", not "poproszę kawa".
Where this fits in
Food & ordering, Polish A1: Order at a café or restaurant, ask for the bill, and talk about basic food and drink.