How many ways are there to say good bye and hello? Like dag! Or doui (however you spell that)
Meeting: dag (hello and goodbye), goeiendag, goedendag, hallo, hi, hije, he, hoi. Parting: doei, doeg, tot ziens, tot zo, groetjes, adieu, ajuus, ciao, houdoe.
There are more regional greetings that I am not very familiar with. They use different greetings in the provinces of Friesland and Limburg. Most of these greetings are informal and you may find even more than what I can think of.
Good morning, good evening and goodnight also have different forms. Even sleep well (welterusten) is used as a goodbye greeting.
That's what comes to mind at this moment.
For a beginner, it is maybe useful to stick to a small number of greeting expressions.
When you meet somebody, you can say:
formal: goeiemorgen (goeiemiddag, goeieavond) (in NL and B)
widely used: hallo (in NL and B)
informal: hoi (in NL) or hi/hé (in NL and B)
To say goodbye:
slightly formal: dag (in NL; less formal in B) (often pronounced as 'da-ag', as if it were two syllables)
widely used: tot ziens (in NL and B)
informal: doei (in NL); in B you will often hear 'salukes'
As Hermina pointed out, there are a lot of regional expressions, but with the above mentioned words you will do just fine.
NB. You will also see the more formal spellings 'goedemorgen, goedemiddag, goede(n)avond'
Here you go:
Generally the way people say hello or goodbye depends on personal prefernce, formality level and the region.
Where I live you hear: doeg, doe, ajuu, ajuus, tot kijk and joe. (those are the more popular ones)