"Tomorrow in the afternoon"
Translation:Amanhã à tarde
It's a contraction of "a+a", being the first a preposition and the second a definite article.
In this sentence, you can see "a = in" and "a = the", thus "in the = a+a = à"
Please remember that "in = a" only in this case. Prepositions should always be translated with the entire expression to make sense:
- Vou à praia = I'm going to the beach (to + the = a + a = à)