how to apply design patterns when we get a new project?

first of all if a client approach to do a project.gather the requirements
and find which type of application he wants
for example if he wants his application to connect with the internet then you have to use the asp.net technology to develop your application.
otherwise another type he wants standalone application like games,antivirus softwa re then you need to choose design pattern of windows application .

Exactly like Siva said,You need to collect the requirement from the client.
According to the requirement you can decide Whether need to do it as a web application or as a desktop application.

ok . can i have a sample scenario showing the requirement and the design pattern applied to that.
i mean let s say a shopping online asp.net application, it will have normally catalogue, products , add to cart and billing ..
this is the general functional modules in a shopping online application.
now how do we analyse on which design pattern to apply for this.

have you already familiar with any design patterns?

Yes i do. i have gone through abstract method, factory method most popular singleton method.
nothing much like behavioural pattern and so on. but interested to know about that too.
i have no experience in how to implement the method with the received requirement. i mean how to decide what type of design pattern can be used for this requirement and how to do so..

appreciate explanations.
thanks