I have two queries:
firstly, If i buy the dreamweaver software, then, do i have to pay extra money to exploit all your themes and features? what i mean to ask is whether i will have to pay for any other service once i buy the pregramme.
secondly, can the student discount be used for a particular software like dreamweaver or can i only use it to buy the creative cloud all apps?
Dreamweaver is only available from Adobe via a Creative Cloud Subscription (recurring monthly or annual payments). Adobe no longer sells a "perpetual license" version (one time payment).
There are paid and free extensions and themes available for Dreamweaver to add functionality or design options to the program from various sources across the internet. None are necessary to use the program, though some of the better ones will make life easier for non-coders using the program.
According to Adobe's site, there is no Single App subscription available for students, however a full student subscription is currently a dollar less per month than a standard single app subscription. Creative Cloud pricing and membership plans | Adobe Creative Cloud
Dreamweaver comes with Starter Templates and code Snippets to help you jump start your projects.
Go to File > New > Starter Templates.
Commercial extensions are available from 3rd party vendors if you need them. The vendors I can recommend are: