Learn Hardcore Portuguese (Portugal): Eu quero ganhar um prémio neste concurso.

Portuguese is a pro-drop language, so you can perfectly well say Quero ganhar um prémio neste concurso without Eu. Including Eu adds emphasis or clarity (for instance, contrasting your wish with someone else’s).

What’s the difference between quero and gostaria de here?

Quero is the present indicative “I want,” direct and neutral in tone.
Gostaria de is the conditional “I would like,” more polite or tentative.

Why use ganhar in this sentence? Could I use vencer or receber instead?

Ganhar means “to win” or “to earn” a prize.
Vencer focuses on “coming first” or “beating” the contest (e.g. vencer este concurso).
Receber means “to receive,” which highlights getting something, not necessarily having competed.

Why um prémio and not o prémio?

Using um prémio refers to an unspecified or one among many possible prizes. O prémio would point to a specific, known prize (e.g. “the grand prize”).

Why is it spelled prémio with an accent on the “é”? I’ve seen prêmio too.

In European Portuguese, the standard spelling is prémio (acute on “é”).
In Brazilian Portuguese, it’s prêmio (circumflex on “e”). The pronunciation differs slightly as well.

What does concurso mean? Is it the same as competição?

Both words mean “competition/contest,” but:

Concurso often implies a more formal contest (e.g. art, writing, exams, job applications).
Competição is broader and often used for sports or general competitive events.

Why neste concurso? What is neste?

Neste is the contraction of em (“in”) + este (“this”), masculine form, matching concurso. So neste concurso = “in this contest.”

Could I say nesse concurso or no concurso instead of neste concurso?

Nesse = em
- esse (“in that”), used for a contest you’ve already mentioned or that’s farther from the speaker.
No = em
- o (“in the”), neutral article without pointing to “this” or “that.”
  All are grammatically correct but convey slightly different deixis/context.