HELP | calling functions from controller

Hiya all,
I have worked with codegniter previously and just came back to it now and I guess im a bit rusty.

I can't figure out the following problem:
What is the best solution to call functions from a view (lets say I want to move to a new page from page X, which is a PHP page that uses SQL queries that I have on controller X)? 

example:
From my homepage I want to move to the 'Library' page (which uses a custom SQL script).
When I use href it won't load the script.
The controller function that calls for the model function with the SQL query is there but it wont load (also with  window.location.href="<?php echo site_url ) 

So how do I do it?

thanks!