Stripnulls Explanation

[Knowledge_is_Et]

Function StripNulls(OriginalStr As String) As String
If (InStr(OriginalStr, Chr(0)) > 0) Then
OriginalStr = Left(OriginalStr, InStr(OriginalStr, Chr(0)) - 1)
End If
StripNulls = OriginalStr
End Function

Ok, I know what that does, but I'm not so familiar with string functions, so... how does it work... and why do I get nulls from c++ but I can't add nulls to a string? like:

for I = 0 to 10
stringname = stringname & null (or vbNull?)
next i