Pretérito Perfeito Simples vs Composto in Portuguese

In short, the Pretérito Perfeito Simples is used to talk about complete actions, whereas the Pretérito Perfeito Composto (aka Preterite) conveys an ongoing temporal quality, particularly when something has been taking place lately. Read on.

The English equivalent of the Pretérito Perfeito Simples is either the Past Simple or the Present Perfect (depending on contextual subtleties). 

Here are a couple of examples: 

[complete action]
Ele arranjou o carro dele.
He has fixed his car.  (Present Perfect)

Hoje tomei o pequeno almoço às 9h.
Today I had breakfast at 9 am (Past Simple)

Conversely, the English equivalent of the Pretérito Perfeito Composto is the Present Perfect Continuous: 

[ongoing action (lately)]
Ele tem estudado muito.
He has been studying a lot.

Now, this can be counterintuitive because the Pretérito Perfeito Composto is analogous to the Present Perfect concerning structure, but that’s about it. Either conveys distinct temporal qualities: ongoing vs complete actions.

So, the following sentences 

Ele tem estudado muito. (ongoing action)
He has studied a lot. (complete action)

may match in structure – auxiliary verb [ter/have in the Present tense] > main/action verb  [Past Participle] – but they don’t match in their temporal qualities.

To summarize, here are the temporal-flow matches between Portuguese and English:

[complete]
Pretérito Perfeito Simples → Past Simple/Present Perfect
[ongoing (lately)]
Pretérito Perfeito Composto → Presente Perfect Continuous