Both are same and it does the same action.
Most (but not all) worksheet functions can also be called from VBA. For example, you can use the VLOOKUP worksheet function in VBA by calling Application.WorksheetFunction.VLookup
(or Application.VLookup).
Similarly, you can use Application.WorksheetFunction.Find and Application.WorksheetFunction.Search
. You can use them to emulate the way the worksheet functions work in your VBA code.
These functions are only available in Excel VBA, whereas InStr is a generic VBA function, available in all Office applications (and in VB6, VB.NET etc.)
Apart from that, the Range object in Excel VBA has a Find method, and the Worksheet object has a Find object. These, however, serve a different purpose: you can't use them to search for text within a string, but to search for cells with specified content.