Turkish marks plural once. If a number or a quantity word is already there, the noun does NOT take -ler or -lar: iki kitap, not "iki kitaplar". The plural ending is only for an unspecified many.
Examples
- İki kitap aldım.
- I bought two books.
- Üç kardeşim var.
- I have three siblings.
- Çok araba var.
- There are a lot of cars.
The mistake to avoid
Adding the plural after a number is the commonest beginner error - the number has already done that job.
Where this fits in
Numbers, days, time, Turkish A1: Count, talk about days and months, give the time, and handle numbers in real situations.