How to create subscribe function for register user for news portal

Although it's all depend on you how the logic for the subscription to be built but you may follow the typical logic that many portals have followed.

1. Have a subscription tab/form/link/section where you can capture information of the visitors of your website. The minimum information you need for subscription is an email id. Other optional information you may like to capture based on your requirement are-
a. Name
b. Country (If you are publishing country specific news)
c. State (If you are publishing state specific news))
d. Language (If your website is multi-lingual)
e. Mailing frequency preference
f. Time preference for getting mails
g. etc.

2. Have a table that captures all these information
3. The subscription can be of two types (minimum) for news kind of websites. Either you can send a news as a mail to all your subscribers as soon as it is published or/and you can send them an hourly/daily/weekly news letter.
4. If you want the news to be sent immediately then you may create a background process which will send these mails to the subscribers as and when a news is published.
3. If you want to send mails like news letters you can create a windows service / or a program that is scheduled to run on specific time of the day.
4. You need to have a table which contains the news letters which you can create or build such a dynamic logic to create themselves.

You can change the logic according to your requirement.

Hope, it helps :)