*DUM DA DUM native english person living in the Netherlands to the rescue*
Tarbicus is quite correct about a good english approximation of dank u wel.
The "a" in dank should be pronunced a lot like in the word ankh, the egyptian symbol for life. Wel is just like it sounds. the "u" sound is sort of made by saying oooo (as in ooooh aaah) and compressing your lips into a tight circle. Kind of like the first part of "oops", but putting more u sound into it.
The easiest solution is to just use dankjewel instead. That is the informal variant (as opposed to the other which is formal). It is also easier to say: instead of the dutch u sound which can be hard for foreigners, you just make a soft y sound, like in the word yes. There are very few people especially these days who will care or even notice if you use the informal thank you.
As for the word hello, the word "hallo" will work just fine. Most Dutch people are really quite casual. You'll sound very formal if you go around saying things like goedemorgen, for example-- and hallo is very easy.
For good-bye, dooi, dag, or tot ziens, works great.
Pronounced as follows (more or less):
doei-- du-WEE
tot ziens-- TOT zeens
dag-- dAAA (pull out the short a sound here) + the dutch g which is very hard for english speakers to do-- it is sort of a gutteral sound you make in the back of your throat... sort of the sound you make when you are choking, but toned down a lot.... if you can't do it, then stick to one of the others.
One more useful one is alstublieft which means either "please" or "your welcome" depending on the context. The rules on where and when to use this aren't very clear to a native english person in my opinion, so you just have to learn when to. The most clear use is to say it whenever you give something to someone (eg. giving the conductor on a train a ticket, or giving money to a cashier, but really anytime you are handing someone something and want to be polite, It's sort of a "please take this" kind of phrase).
As a warning, Dutch people NEVER pronounce it how it is spelled or even should be pronounced, they slur it so much that it comes out totally different. Here's the pronounciation that everyone will be used to:
alstublieft-- aaa(long short a) + sh + u(very short u) +bleeft.
That's probably enough. A few polite Dutch words here and there will please most Dutch people (they appreciate you using their languaged a bit), but more than that is not needed. Most everyone speaks english better than you, and if you try more Dutch than that, you will either be mistaken for knowing more than you do and be up a creek without a paddle, or more likely be spotted as foreigner in 5 seconds and be addressed from then on in English. The Dutch are very practical and don't like wasting time, so they'll always switch to the fastest and most efficient means of communication. They don't want to spend twice as long listening to you butcher their language.
