How to change the title tag without modifying the site name?

As the question begs, how can I change the title tag (<title>Title Goes Here</title>) without altering the site name (settings>general>site title)?

About my site and what I want to accomplish with this question:

-I’m not using an image as my logo.
-I don’t want to display the same ‘static’ title in every page.
-I want to use seo without the use of plugins.

By the way,
-I also want to be able to create a meta description tag. How do I go about that?

Thanks, in advance, for your help!