。
Put the tomato salad in the refrigerator.
Literal
Refrigerator [of-の] inside [in-に] tomato-salad [object-を] put [imperative-なさい].
The 入れる ('put in') + に direction pattern. Two loanwords: トマト (tomato, Portuguese origin via Spanish, actually Nahuatl originally — Japanese borrowed via European contact) and サラダ (salad, via English). 入れなさい is the ~なさい polite imperative.