In English it's pretty simple: something or nothing.
The Portuguese options are (surprise) numerous and confusing. Let's break-these-down and make these more user-friendly.
You've learned alguma coisa, right? And that's clear: alguma (some) coisa (thing) = something.
But you rarely hear Brazilians say that. There are other options they favor - most depend on what the something is. I'm tempted to list here all of the different ways they'll express something, anything, nothing but that's more frightening than helpful. Let's look at the main, most-used ways these are said.
Something in Portuguese
If you're just saying something - not referring to anything at all, use alguma coisa.
Dúvida: What about alguma coisa vs. algo?
Resposta: Don't worry about whether to use "algo" or, "alguma coisa" -- USE EITHER.
It's more common that you're talking about something specific. In this case you probably also know what the gender: some work, some beer, some girls, some people. Brazilians like to use the pronoun "a". When used in the plural the meaning shifts. Like this:
uma coisa = a thing
umas coisas = some things
uma praia = a beach
umas praias = some beaches
uma pessoa = a person
umas pessoas = some people
The "a" turns into a "some" in the plural. We don't have a plural "a" in English. We actually say "some".
um homem = a man
uns homens = some men
um político = a politician
uns politicos = some politicians
um táxi = a taxi
uns taxis = some taxis
The second common way is to use, algum. Like this:
some men = alguns homens
some people = algumas pessoas
If you can get used to these above forms you're golden.
Nothing in Portuguese
If you're just saying nothing - not referring to anything at all, use nada.
As a second choice or, to add emphasis:
I would just default to nada - even in this example:
Anything in Portuguese
Always use qualquer coisa with variations. Like this:
And what about somewhere, anywhere and nowhere?