Learn English – “How much it cost?” or “How much does it cost?”

OP's example Internet (without the definite article) is a distracting non-standard usage. See “I don't have internet” vs. “I don't have the internet” as previously asked on ELU for further discussion of this).

So to focus on the specific aspect of usage being asked about here (using "do" to frame a question), let's change it to...

1: How Facebook helps you
2: How does Facebook help you?

Notice that in my amended version, I've removed the question mark from #1. That's because it's not a question. It's not even a sentence - it's just a noun phrase. We can see this by considering...

Quantum physics is a complex subject (Noun Phrase + Verb + Noun Phrase)
He explains quantum physics (Pronoun + Verb + Noun Phrase)
He explains how Facebook helps you (Pronoun + Verb + Noun Phrase)

As to whether it's necessary to include do in questions, consider this answer to the earlier ELL question “How it works?” vs. “How does it work?”. Effectively it's not, since these are all valid questions...

How can Facebook help you?
How will Facebook help you?
How could Facebook help you?
How has Facebook helped you?
How is Facebook helping you?
etc., etc.

That's to say, the interrogative (how, in this case) must be followed by an auxiliary verb, but there are many others besides to do that can perform this function in questions.

I would skip referring to "gigabytes" entirely:

How big a hard drive do you need?

And if you are a customer, you ask

What's the biggest drive on the market?

To my (AmE) ears, it seems odd to ask about the number of gigabytes; the thing I'm interested is the size of the drive, and I'd only talk about that until it comes time to specify a number.