Learn Hardcore Portuguese (Brazil): O comando está claro.

Comando is a masculine singular noun, so it normally takes the definite article o when you are talking about the command in a specific context.

o comando = the command
um comando = a command

In Portuguese, articles are used more often than in English, so leaving out o would usually sound incomplete or unnatural here.

What exactly does comando mean in this sentence?

Comando usually means command, but the exact sense depends on context. In Brazilian Portuguese, it can refer to things like:

a computer command
a military command
an instruction or directive
a control mechanism in some contexts

So in this sentence, it means the command or the instruction, depending on the situation.

Why is it está instead of é?

Portuguese has two main verbs for to be: ser and estar.

Here, está is used because claro is describing a current state or condition: the command is clear right now.

está claro = it is clear / it’s clear
é claro often means it is obvious, of course, or describes something in a more general way

So:

O comando está claro. = The command is clear.
É claro. = Of course. / It’s obvious.