first of all: https://wiki.openoffice.org/wiki/Extensions_development_basic is a good starting point. In particular the XRAY tool is very helpfully.
The following code shows a search example:
Dim oDoc As Object
Dim oSheet As Object
Dim oSearchDescriptor As Object
Dim i As Integer
oDoc = ThisComponent
oSheet = oDoc.Sheets(0)
oSearchDescriptor = oSheet.createSearchDescriptor()
oSearchDescriptor.SearchString = "is"
For i = 0 to oDoc.Sheets.Count - 1
oSheet = oDoc.Sheets(i)
oResults = oSheet.findAll(oSearchDescriptor)
'xray oResults
if not isnull(oResults) then msgbox oResults.AbsoluteName
Next i
If you have XRAY installed, you can inspect every object with it and you have access to the related API docs.
Greetings
Axel