"वह सेब काटती है।"
अनुवाद:She cuts the apple.
Use 'the' when there is one particular thing you are talking about. Now lets talk about the sentence "she cuts the apple." Here, I would notice that she have specific thing which the apple means only one apple , she don't have many choices among it , if she has plenty of choices then she can say like that "She cuts an apple" (choices are like mango,banana,orange etc).