It's common to start a sentence with a form of the verb "to be," to get the sense of the English "there is" / "there are" structure.
Sunt umbrae in silva.
I put: "in silva sunt umbrae" ... and it told me this was wrong. It told me the correct solution was: "There are shadows in the forest" ... which was the English sentence (reported)
Also, your ordering of the Latin sentence is nicer than the suggested one.
Silva - a forest
Sylvestris, sylvestre - related to a forest