Can you tell me in detail about .qfl & .vbs extensions that are used for QTP files ?

In QTP normally we use three different types of extensions.
.QFL is local to the QTP and will be called and also used by only QTP.
Where as .VBS & .TXT files can be used by QTP and as well as other application as well.

And one more difference is in QFL you can put a break point, where as in .VBS you can not put a break point.
In general all of these three extension files can be used to define a function and then use this file(function) in QTP.

And the last difference is .QFL files you need to associate with test to call it. But .VBS functions you need not associate them to the test you are calling from. You can simply use executeFile statement to call vbs file.