How to create internal and external links In drupal 4.x, in contents, links are created like this
[url=1]Some text[/url]
So when "Some text" click it open node 1.

Sometime it may link to external url also. like below:
[url=http://www.abc.com/somepage.html] external link [/url]

same thing how can i do it in drupal 7.x
To be honest, I don't know anything about Drupal 4.  I don't regard it as a platform to build on in 2014.

In Drupal 7, out of he box, you create links using plain HTML:

&lt;a href="/node/42" title="internal link"&gt;internal link&lt;/a&gt;
&lt;a href="http://example.com/somepage.html" title="external link"&gt;external link&lt;/a&gt;


There are a bunch of modules for Drupal 7 you can install that gives you other syntaxes for adding links to content. To mimic the square brackets around tags syntax you cite as example. Install the Bbcode module.  It uses markup based upon BBCode.  For a more modern style, similar to StackExchange, install the Markdown filter module. It let content authors use markup based upon John Gruber's Markdown.