Kore, sore, are, dore
You're probably heard at least some of these terms before if you've ever listened/read/over heard/etc any Japanese as these terms are quite common, as as their English meaning is in English. Let's go through them one at a time.
"Kore" means "this" and is used when referring to things that are close to the speaker (and often when they are holding the item or standing very close to it). The particle "wa" always comes after it. (Least as far as I know. I have yet to encounter a case where this isn't so.)
Kore wa nan desu ka?
What is this?
Kore wa ikura desu ka?
How much is this?
Ikura = how much (as in amount of money)
"Sore" means "that" and is used when referring to things that are further away from you but still relatively close. (Often to something close to the person you are speaking to; "that thing in front of you")
Sore wa watashi no kasa desu.
That is my umbrella.
Sore wa anata no enpitsu desu ka?
Is that your pencil?
Don't get this confused with "sore"! They are two different things!
"Are" means "that" as in "that over there". It is something that is far away from both you and the person you are talking to. There is no limit on the distance, it could range from a few meters to a few miles to even farther.
Are wa ginkou desu ka?
Is that (over there) a/the bank?
Are wa samu-san no jitensha desu.
That (over there) is Sam's bicycle.
"Dore" means "which" as in "which one?" or "which do you like?".
Dore desu ka?
Which is it?
Dore has some more complicated uses, but for now we'll keep things simple. Question words like "dore" and "nani" cannot be followed by the particle "wa" but instead be followed with "ga". (I'll go more into detail about why that is at a later time. But for now, you'll just have to remember this.)
Dore ga anata no pen desu ka?
Which one is your pen?