Questions & Answers about Они налили вино.
Налили is the past tense plural form of the verb налить, which is a perfective verb.
In this sentence, it means they poured or they poured some.
The perfective aspect suggests a completed action: they finished pouring the wine.
Compare:
- они наливали вино = they were pouring / used to pour wine
- они налили вино = they poured the wine / they poured some wine
In Russian past tense, verbs agree with the subject in gender and number.
The ending -ли shows that the subject is plural.
So:
- налил = he poured
- налила = she poured
- налило = it poured
- налили = they poured
Because они means they, the verb must also be plural: налили.