In web page, link is initial and most important tag. Basically link is called webpage. So in the grails , we can easily as like.
In the site/index page, add following link which redirect to about page
<h4>About Page : <g:link controller="site" action="about">Go To About Page</g:link> </h4>
In the site/about page, add following link which back to home page
<h4>Home Page :<g:link absolute="true"> Home Page</g:link> </h4>
You can create different way this link in grails. For more, see - http://docs.grails.org/3.0.17/ref/Tags/link.html