Will not coverNot relevant to WordPress.com:Installing/hostingWordPressPluginsDNS ChangesEditing HTML and CSS
Why do you want a site?
WordPress.comBasic service is freeIt’s much easier to setupEverything is taken care of: setup, upgrades, spam, backups, security, etcLimited in what you can doWordPress.orgFree, open source softwareYou can do much more with it (flexibility)You have much more control (and, hence, responsibility)Harder to setup and manage – but there are options (e.g. one-click installs)