The two “extra” holes are usually on a “long foot” flute and are what would be covered by the low C# and C natural keys on an 8-key flute - some folk reckon having the “dummy” long foot improves or at least affects the tone colours and response of the flute; others disagree. IMO it doesn’t matter - I wouldn’t choose not to buy a flute because it was either one or the other (but then, I wouldn’t normally buy an unkeyed flute! 
) - how it played overall would matter more. But you’re right, you only cover the normal 6 tone-holes, 3 with each hand and you only get a scale down to bottom D. (And you don’t count the embouchure hole, of course!)
Your best way to learn about flutes apart from reading this Forum and asking questions (most beginner questions have been asked and answered umpteen times, so use the Search facility before asking!) is to browse the Makers List - read a maker’s website or four every day and work your way through the lot - at the end you’ll know a load more about flutes, who makes what and why… and who you might be interested in buying one from in due course… if you don’t decide to go for an antique (with luck and sound advice you can get a reasonable intermediate player’s renovated antique 8-key for similar money to a keyless new-made by even the cheaper modern makers…).
Welcome aboard!