What is the difference between "flera" meaning several, and this "fler" meaning more??? How would you ask if someone wanted several pillows then?
Roughly, fler is used for number and mer for amount.
As for your second question, that'd depend on what you meant. You could say "Vill du ha några/ett antal/fler kuddar?" for example.
Okay, that makes sense, about things that are countable vs things that aren´t.
I found this article useful: http://www.thelocal.se/blogs/theswedishteacher/2011/01/24/mer-mera-fler-or-flera/
Vill du ha fler gudar? The pronounciation on last word needs to be improved.
Interesting. I find that the first three words are said rather simultaneously, sounding somewhat like "Vilda fler kuddar?"
I thought more was mer. I now Emil said fler is for number and mer is for amount, but im still confused.
Fler for countable things, mer for uncountable.
In this case, you can have one or two pillows, but not one or two sugars.
It is also basically the same as when using många or mycket.
Sorry if this is a silly question: Why is it "ha" not "har" in this sentence?
You have to use the infinitive, not the present tense ("har"). This is true for English too, but since English rarely marks the difference it's not as visible. But it is comparable to the fact that you would say "He would like to have some more" and not "He would like to haves some more".