>Kindly let me know what is dll, API and fll files ? How can I create it and how can we use this in project ?
>
>Second, what is function of installsheild ? how can I use it. I would appreciate if anyone could explain me in detail and if possible to explain it with examples.

Saif,

DLL: Dynamic Link Library is a set of programs or routines packages as a separate library (generally using COM but not always so). You can create them in a variety of programming languages, including VFP (see the dialog in the Build section of your Project Manager).

FLL: a special kind of library only used by FoxPro (generally in older versions than VFP). You need C++ to build them. Not used much nowadays, except for FoxTolls.FLL that still has a few remaining useful routines.

API: Applications Program Interface. When you read API in a FoxPro contect it generally refers to the Windows API.

InstallShield is an installation program to package and diastribute your EXE and other needed files (runtimes, ActiveX, DLLs, etc.)

See: "Walkthrough: Creating a VisualFoxPro Application Setup Program Using InstallShield Express" by Mike Stewart [MS]
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnfoxgen7/html/vfpdeploy.asp