Work with legacy and simple sites using jQuery selectors, events, AJAX, effects, and plugins.
Lessons
Pick a single element from a matched set by position.
eq(), first() and last() is easiest to learn by reading the example, changing it, and observing the result.
$('li').filter(':even').addClass('striped');
$('li').not('.active').css('opacity', 0.6);
$('tr').eq(2).addClass('selected'); // third row (0-based)
$('li:contains("PHP")').addClass('match');Practice the eq(), first() and last() example in a small scratch file, then explain what changed and why.