XML : On understanding blogger template macros and sections

What's the difference between <b:section-contents id='xx'> and <b:section>? Or

   <aside>     <macro:include id='main-column-right-sections' name='sections'>       <macro:param default='2' name='num' value='1'/>       <macro:param default='sidebar-right' name='idPrefix'/>       <macro:param default='sidebar' name='class'/>       <macro:param default='true' name='includeBottom'/>     </macro:include>   </aside>    

What's aside for in this context? What is macro? How do these things affect the templates?