Hi Danish,
I'm not quite sure what you are asking. On the Customers and Contacts List screen you can enter the name of the contact you are looking for into the Contact/Customer/Company filter field (see my screenshot below). From here you can click the Go To... link to see all of the fields related to the customer and contact that you selected.
If you would like to make a screen where you can select a contact from a dropdown, and have their information automatically populate some fields, you can look into how this is done on the stock Estimate screen. There are some actions in the Customer:Job dropdown field that are triggered upon a Text Change event. See below:
We don't have step by step instructions on how to customize something like this, but feel free to get in touch with an in-house consultant or a Method Solution Provider.
Jason