I have been asked these questions and didn't always have an answer to them right away. I thought it would be interesting to document some of these so they may be helpful for you in the future. Note:The answer is in no way always the best/right, just my best attempt.
Here is first one: How to set position of DIV?
Answer: There are three position options in css,"absolute", "float" and "relative" Examples as below.
<p> in a div</p>
<div style="float: left; width: 50%; height: 100px;"></div>
<div class="background" style="position: relative; width: 728px; height: 200px;">