O goleiro pode defender bem.

O is the masculine singular definite article, meaning the.

• o goleiro = the goalkeeper
• Portuguese usually uses articles more often than English does.

So this sentence is talking about the goalkeeper, not just a goalkeeper or goalkeepers in general.

Goleiro is the usual Brazilian Portuguese word for goalkeeper or goalie.

In Brazil, it is especially associated with soccer/football. In other sports, people may still understand it, but the strongest association is soccer.

Poder is the infinitive, meaning to be able to / can.

Here, the verb is conjugated for ele/ela/você and also for noun subjects like o goleiro:

• eu posso = I can
• você/ele/ela pode = you/he/she can
• o goleiro pode = the goalkeeper can

So pode is used because the subject is o goleiro, which is third-person singular.

After a modal verb like poder, the next verb normally stays in the infinitive.

So the structure is:

• pode defender = can defend

This is similar to English:

• can defend
• not can defends

Bem means well here. It is an adverb modifying defender.

• defender bem = to defend well

So it describes how the goalkeeper defends.

In Portuguese, adverbs like bem often come after the verb.

So:

• defender bem = defend well

This word order is very natural in Portuguese. English also does this often, so it is not too different here.

Yes. Pode can express:

• ability: can
• permission/possibility: may / can

In this sentence, with o goleiro, the most natural reading is ability:

• The goalkeeper can defend well.

Yes.

• O goleiro pode defender bem = The goalkeeper can defend well / he is able to defend well
• O goleiro defende bem = The goalkeeper defends well / he generally defends well

So:

• pode defender focuses on ability or possibility
• defende states it more directly as a fact or habit

Portuguese often does not need a subject pronoun when the subject is already clear.

Here, the subject is explicitly given:

• O goleiro = the goalkeeper

So there is no need to add ele.

Portuguese commonly uses either:

• a noun subject: O goleiro pode...
• or a pronoun if needed: Ele pode...

It can mean to defend/protect, but in soccer contexts it often has the more specific sense of:

• to save
• to stop shots
• to make saves

So with goleiro, defender bem often sounds like being good at saving shots, not just defending in a general sense.

A simple approximation is:

oo go-LEY-ro POH-jee deh-fen-DER beng

A few useful notes:

• O often sounds like oo in Brazilian speech.
• goleiro has the stress on lei: go-LEI-ro
• pode in Brazil is usually pronounced roughly POH-jee
• final -r in defender is often soft in Brazilian Portuguese
• bem has a nasal sound, roughly like beng but nasalized

Yes, defender is a regular -er verb.

A few present-tense forms:

• eu defendo
• você/ele/ela defende
• nós defendemos
• eles defendem

That makes it easier to learn, because it follows the normal -er pattern.