From your description of what you want:
I guess you hide the text first,
Then show the text in a “scroll” JS event handler, https://api.jquery.com/scroll/
E.g.:
jQuery(document).ready(function($) {
$('.target').css('left', '-9999em');
$(window).scroll(function() {
$('.target').css('left', '0');
});
});
You could increment the ‘left’ value so that it gradually appears in view, then use CSS transitions to animate it.
If that’s not what you want then you need to describe what you want in more detail, however, I don’t think this is a WordPress issue. jQuery forums can be found here: https://forum.jquery.com/
