This is the 627th most frequent Japanese word.
ミルク
Milk.
Here, 'ミルク' (milk) is used as a noun to refer to the milk that is added to coffee as an ingredient.
私はコーヒーにミルクを少し入れます。
I add a little milk to my coffee.
Here, 'ミルク' (milk) is part of the compound noun 'ミルクティー' (milk tea), denoting a beverage.
このお店のミルクティーはとても美味しいです。
The milk tea at this shop is very delicious.
In this sentence, 'ミルク' (milk) is used as a noun to indicate milk prepared, presumably for drinking.