what kind of problem you can have when installing Local Area Network (LAN) at a client places?

You can run into many issues if you are not familiar with LAN technologies. Setting up a LAN is not a "plug-n-play" technique.

Generally, what JorgeM said is correct. However, for simple LAN configurations it can be pretty much PnP (Plug and Play). IE:

Internet <-> Router (dhcp server) <-> switch <-> computers

This assumes that the computers are all configured to use dhcp to get network addresses (normal default). Issues arrise when you need a LAN-based system to be a local or internet-facing server. Then, it starts to get complicated... :-)

Internet <-> Router (dhcp server) <-> switch <-> computers

My exprineced has been that even for those who even have just a little bit of pc and maybe some very basic networking (as little as plugging in cables), this part of the implementation can be confusing...

So, @Jeetun- what is your experience with PCs and Networking? What are you trying to implement? If you provide some details, you can get better advice from us.