Edit: I'm not sure this will help, but I'll try: I am asking "what's the whole idea with wheels?"; a list of wheel parts is not what I am after. /edit
I'm aware that SPSite - despite the confusing use of a singular noun - represents a site collection, whereas SPWeb represents a (SharePoint) web site.
In order to begin getting a grip on SharePoint I thought it prudent to understand what these two things are. The MSDN documentation got me to the above understanding and not an inch further.
Googling "spsite vs spweb" leads to posts on here with nice diagrams showing how the site collection contains a root web site that is itself a website collection (since it may have subsites) and this bit is very clear.
What is not at all clear is why the makers of SP would bother to do it this way. Since SPWeb is in fact both a web site and a collection of web sites, what need is there for the site collection concept? What is it for?
I realize that it may be difficult to know if your understanding of these concepts is objectively accurate - it is inherently imprecise. Still, I would much appreciate if someone could give me some feel for these core concepts either by explaining in their own words, or by pointing me to someone else's words.