The adverb onde indicates a location.
Onde fica a tua casa? Where is your house?
Onde ouviste isso?Where did you hear that?
Onde can be used to replace expressions such as «em que» and «na/no qual», shown below.
É a gaveta em que estão as chavesIt’s the drawer where the keys are
Lisboa é uma cidade na qual as casas são carasLisbon is a city where the houses are expensive
This adverb is a contraction between the adverb onde and the preposition a. It can be used when the verb both expresses an idea of movement and requires the preposition a (to). It’s most commonly used with the verb ir (go) when asking a question. An example would be:
Aonde é que ele vai? Where is he going?
An answer to this question would involve the same verb + the preposition a (or a variation of it).
Ele vai a Lisboa ~ Ele vai ao supermercadoHe's going to Lisbon ~ He's going to the supermarket
Note: Although there’s a difference between the two adverbs, aonde and onde, aonde is rarely used nowadays. It’s sometimes considered an old and outdated expression, and the grammatical difference itself is subject to dispute. This means you can choose between the two.
Idea of movement
Just as we did with aonde, by combining prepositions with the adverb onde, we can further characterize the movement expressed by the verb. Let’s explore how we can use different prepositions to create a more specific meaning of the concept of “where”.
You can refer to an arrival point or destination using aonde (a + onde) or para onde.
Aonde vais? ~ Para onde vais?Where are you going?
You can see both sentences have the same translation but they’re actually a bit different.
«Aonde vais?» would be a reference to something temporary – for example, an appointment or a 7-day trip. «Para onde vais?», because of the preposition para, gives us a more prolonged sense of time and you’d use it when talking about moving to a different house or city, for example.
While the preposition a is associated with an arrival point, the preposition de is used to reference a starting point. De + onde = Donde.
Donde vens? Where are you coming from?
Não sei donde é que ele apareceuI don't know where he came from
As a process
The process is what’s between the starting and arrival points. You refer to it by using the preposition por + onde = por onde.
Por onde vais? Which way are you going?
Eu vou por onde queroI go which way I want