Even the macro recorder would record the code you need...
Somewhat more sophisticated:
Code:
Sub Demo()
Application.ScreenUpdating = False
Dim StrFnd As String
Options.DefaultHighlightColorIndex = wdYellow
StrFnd = InputBox("What is the text to highlight?")
If Trim(StrFnd) = "" Then Exit Sub
With ActiveDocument.Range.Find
.ClearFormatting
.Replacement.ClearFormatting
.Replacement.Highlight = True
.Text = StrFnd
.Replacement.Text = "^&"
.Format = True
.Forward = True
.MatchCase = True
.MatchWildcards = False
.Wrap = wdFindContinue
.Execute Replace:=wdReplaceAll
End With
Application.ScreenUpdating = True
End Sub