They gave you part of the example out of the help file. You could look there for more info. I was just trying to give you a lead, thinking that you might look it up. But that gives you half the picture, RealToString is the complement. Here is a complete sample.
Code:
Sub testfract()
' Convert the distance to a real in fractional units
Dim unit As Integer
Dim distAsString As String
Dim distAsReal As Double
Dim NewDist As String
unit = acFractional
distAsString = "17.625"
distAsReal = ThisDrawing.Utility.DistanceToReal(distAsString, unit)
NewDist = ThisDrawing.Utility.RealToString(distAsReal, unit, 3)
Debug.Print "17.625 converts to " & NewDist & " in fractional units."
End Sub