Like all Content management systems, WordPress is updated regularly, so the best place to go for the most accurate and up-to-date information is WordPress itself.
WordPress Support
WordPress support has a variety of resources for people new to the CMS. You might want to head straight to Basic Usage for information specifically about using the CMS itself.
https://wordpress.org/support/
WordPress codex
The WordPress codex is the online manual, ‘a living repository for WordPress information and documentation’.