web development concepts frontend backend

I am quiet new developing.... and I'm not quiet understanding everything.

So, for web development you have:

*STRUCTURE:

  -HTML
  -CSS
  -XML
   -For the structure we can use frameworks as bootstrap, foundation...

*FRONT-END LANGUAGES (client-side):

   -javascript
   -jquery
   -ajax
   -flash
   -angularJS

*FRONT-END LANGUAGES (server-side):

   -ASP.net
   -Perl
   -PHP
   -Java
   -Python
   -Ruby

*SERVER (where we host our databases):

    -Apache

*DATABASES:

  -Oracle
  -MySQL
  -Firebird

*CMS (to publish the web): - Wordpress - Joomla

Is it alright? So then..... where should I include DOM....and SEO..?

I don't have this clear at all, so if anyone can explain it to me please.... in a logic way though, because I read a lot about all this concepts but I don't know how to structure them around web development.

Thank you guys!!!!!