O is the masculine singular definite article, meaning the.
It matches oleiro, which is a masculine singular noun:
In Portuguese, articles are used more often than in English, so O oleiro sounds natural where English simply says The potter.
Trabalha is the 3rd person singular present tense of the verb trabalhar (to work).
That form is used because the subject is O oleiro = he / the potter.
Here are the relevant forms:
So:
Na is a contraction of em + a:
So:
This kind of contraction is very common in Portuguese:
Because Portuguese normally uses the article here.
So instead of saying just in workshop, Portuguese says in the workshop:
This is one of the big differences from English: Portuguese often includes articles where English may not.
Here, oficina means workshop, the place where the potter works.
Depending on context, oficina can also mean:
In this sentence, because the subject is oleiro, the meaning workshop is the most natural one.
A rough English-friendly approximation is:
oh-LAY-roo
But in European Portuguese, the final o is often reduced, so it may sound closer to: oh-LAY-ru
Also:
A rough approximation is:
u uh-LAY-ru truh-BAI-lya nuh oh-fee-SEE-nuh
A few useful notes:
Lh is a special Portuguese sound. It is pronounced like the lli in million or the li in some pronunciations of brilliant.
So trabalha is not pronounced like trabala. The ending is more like:
This sound also appears in words such as:
Yes, but it means something slightly different.
O oleiro trabalha na oficina = The potter works in the workshop.
This describes his work or usual place of work.
O oleiro está na oficina = The potter is in the workshop.
This tells you where he is at the moment.
So trabalha talks about working, while está talks about location or temporary state.
It is a real and correct word, but it is not as common as more everyday job words like professor, médico, or empregado.
A learner may not see oleiro very often unless the topic is:
Still, it is a useful word and perfectly natural.