I hope while learning/working on QTP you might have heard about the term "Parameterization".
"Parameterization" : Its a process of passing multiple values(test data/Input Data) for a constant value(Hard Coded) inorder to retest certain functionality/feature.
Data Driven Testing(Retesting) can be done using the Parameterization.
There are 4 types of parameters:
1) Test/action parameters
2) Data Table parameters
3) Environment variable parameters
4) Random number parameters
Test/action parameters :
Test parameters enable you to use values passed from your test. Action parameters enable you to pass values from other actions in your test.
To use a value within a specific action, you must pass the value down through the action hierarchy of your test to the required action. You can then use that parameter value to parameterize a step in your test. For example, suppose that Action3 is a nested action of Action1 (a top-level action), and you want to parameterize a step in Action3 using a value that is passed into your test from the external application that runs (calls) the test. You can pass the value from the test level to Action1, then to Action3, and then parameterize the required step using this action input parameter value (that was passed through from the external application).
Alternatively, you can pass an output action parameter value from an action step to a later sibling action at the same hierarchical level. For example, suppose that Action2, Action3, and Action4 are sibling actions at the same hierarchical level, and that these are all nested actions of Action1. You can parameterize a call to Action4 based on an output value retrieved from Action2 or Action3. You can then use these parameters in your action step.
Data Table parameters :
Enable you to create a data-driven test (or action) that runs several times using the data you supply. In each repetition, or iteration, QuickTest uses a different value from the Data Table.
For example, suppose your application includes a feature that enables users to search for contact information from a membership database. When the user enters a member's name, the member's contact information is displayed, together with a button labelled View
Environment variable parameters:
Enable you to use variable values from other sources during the run session. These may be values you supply, or values that QuickTest generates for you based on conditions and options you choose.
For example, you can have QuickTest read all the values for filling in a Web form from an external file, or you can use one of QuickTest's built-in environment variables to insert current information about the computer running the test.
Random number parameters:
Enable you to insert random numbers as values in your test. For example, to check how your application handles small and large ticket orders, you can have QuickTest generate a random number and insert it in a number of tickets edit box.