When in doubt about which element to use, always refer to the spec. It will tell you exactly where and when it is appropriate to each element(s).
For a section here's is what the MDN spec has to say:
The HTML Section Element (
<section>) represents a generic section of a
document, i.e., a thematic grouping of content, typically with a
If it makes sense to separately syndicate the content of a
element, use an
<article> element instead. Do not use the
element as a generic container; this is what
<div> is for, especially
when the sectioning is only for styling purposes. A rule of thumb is
that a section should logically appear in the outline of a document.
In other words, if you have content that is related and goes together, put them in a section. Example is a heading section. Do this as long as you have actual content that will go in the element and you're not just using it to style your page.
Now for the article element:
<article> Element represents a self-contained composition in
a document, page, application, or site, which is intended to be
independently distributable or reusable, e.g., in syndication. This
could be a forum post, a magazine or newspaper article, a blog entry,
a user-submitted comment, an interactive widget or gadget, or any
other independent item of content.
<article> element is nested, the inner element represents an
article related to the outer element. For example, the comments of a
blog post can be
<article> elements nested in the
representing the blog post. Author information of an
can be provided through the
<address> element, but it doesn't apply to
<article> elements. The publication date and time of an
<article> element can be described using the
pubdate attribute of a
OK so use an article when you have stuff that goes with your site but is independent from the rest of the page. If you use an article element within another element, that article element's content should be related to the parent element's content/stuff.
From what I can tell your
<div class="main"> it for styling and positioning, so it should remain a
<div>. You got that sidebar
<aside> element well, and the content inside is should be in the
<aside> element itself, or if you have content that is groupable and related, then a
<section> element inside that would be appropriate as well.