"Del" and "Al"
In Spanish, when the preposition "de" or the preposition "a" is followed by the definite masculine article, "el," the two combine to become "del" and "al":
Incorrect: Estoy en camino a el cine.
Correct: Estoy en camino al cine.
Incorrect: Eso es el carro de el policía.
Correct: Eso es el carro del policía.
Remember, you only need to do this with the "de" + "el" and "a" + "el" combinations; no other definite article forms contractions like this.
Check out this article for additional insight into these common contractions: