Learn Polish: Mój syn ma rok. Kupiliśmy tort i świeczkę. - My son is one year old. We bought a birthday cake and a candle.

In Polish, you don't say that someone "is" an age. Instead, you use the verb mieć (to have). So, mój syn ma rok literally translates to "my son has a year".

Where is the word for "one" in ma rok?

You usually don't need to say jeden (one) when someone is exactly one year old. Just saying ma rok (has a year) perfectly expresses "is one year old".

How do we know who bought the cake just from the word kupiliśmy?

The ending -śmy tells us the subject is "we". The -li- part shows it is in the past tense and that the group includes at least one male (for example, a mother and a father). If it were a group of only females, it would be kupiłyśmy.

Why is the word for candle spelled świeczkę instead of its dictionary form świeczka?

Because it is the direct object of the verb kupiliśmy (we bought). Feminine nouns ending in -a change their ending to -ę when an action is being done to them. This grammar rule is called the accusative case.

If the candle changes to świeczkę, why doesn't tort (cake) change its ending?