>Would you mind to introduce the functions of DCOM?
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DCOM is the mechanism that allow you to access COM servers running on other machines in the same way that you access out-of-process and in-process COM components that run on your machine. DCOM stands for Distributed COM (COM = Component Object Model.)

>When i look at those mentioned DCOM, it seems to be a communication utility. What is this actually doing?
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It repackages property and method references from your app and routes them to the appropriate COM server across the network interface (the process of accessing properties and methods by sending mesages to the COM interface, regardless of whether within the current process, across a process boundary, or across some sort of network boundary is called marshalling), and brings the results back to your machine. From your application's perspective, the COM server is used the same way it would be used if it ran locally as another program, or as a part of your own program; DCOM provides the inter-machine message passing for you so that you don't have to deal with it in detail in your own application. You just access properties and methods of the COM server.

>Furthermore, i want to set up a "Server" letting several other "Clients" to access and to query some data online. What should i do this achieve this goal?
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Depending on what you want to do, you may want to write a COM server that can service multiple clients through DCOM as remote servers, or use MTS or another server pooling tool to manage a set of COM servers, or it might be that all you need to do is make a database available through a database back end. I'd start by reading Chapter 16 of the VFP6 Programmer's Guide Adding OLE to see if you need or want to use COM as a mechanism for your application, and if you do, what type of COM environment is needed, and how it will be accessed.