It is a spelled as: 'ie.
For example: Hoe rijdt 'ie?
A high comma is used, just like you do with some English words. Like "You're".
It simply means 'Hij" (He).
It is informal, but can be used widely in conversations.
Other versions:
Het (It) = 'T
Haar (Her) = D'r
Zijn (His) = Z'n
Zij (She) = Ze