Difference between relative and absolute paths in css

Question

I am a beginner in CSS.And I working with "div id's".I am so confused about this topic.can anyone explain clearly about these "div id" and "class" topics and also Difference between relative and absolute paths in css.

Answer 1

id must be unique for each element.
with class you can groups elements to set them same style

Answer 2

can you explain them with examples

Answer 3

.red{
background-color: #f00;
}
.text-green{
color:#0f0;
}
.text-white{
color:#fff;
}

<!--. HTML. -->

<div class="red text-white">
this text must be white
<p class="text-green">
Some text. And its green
</p>

</div>

<ul>
<li class="text-green">
im green
</li>
<li class="red">
red bg
</li>
</ul>