Internal links

hello,

i want to know how to use the internal links. It should be explained but i´m not ennglish and i don´t know how to search that.

For example when you enter to this subforum the link shows http://wordpress.org/support/forum/3 but when click “add new” button go to the bottom and the link shows http://wordpress.org/support/forum/3#postform

hope you understand. Thanks and bye