nav.to is a function that in5 creates & uses for navigation. nav.to(1) takes you to the 1st page.
window.top ensures that the added code works if its nested in an iframe somewhere.
Bookmarks are stored in the data-bookmarks attribute. The code searches for the string in the bookmark name.
index() gets the position of the page in the document, but it's zero-based, so add a 1 to work with the nav.to function.
There are several issues with the code in your comment. Use this instead:
function goToBookmark(bname){
window.top.nav.to($("[data-bookmarks*='" + bname + "']").index()+1);
}
$('#mission').click(function(){ goToBookmark('mission'); });