Learn Hardcore Portuguese (Brazil): Eu vou chamar o técnico agora.

In Brazilian Portuguese, subject pronouns are often optional because the verb form already shows who is doing the action. Vou already means I am going to, so eu is not required.

You might include eu:

for emphasis
for contrast, as in Eu vou chamar o técnico, não você
for clarity in some contexts

In everyday speech, leaving it out is very common.

Why does Portuguese use vou chamar instead of a single future form?

Vou chamar is the very common spoken way to talk about the near future in Brazilian Portuguese.

It is built like this:

vou = I go / I am going
chamar = infinitive, to call

So literally it is something like I am going to call.

There is also a simple future form:

Chamarei o técnico agora

That is grammatical, but in everyday Brazilian Portuguese it sounds more formal, written, or less conversational. In normal speech, vou chamar is much more natural.

What exactly does chamar mean here?