Your WordPress site is built on two different content types: Posts and Pages. They are very similar in functionality so I will list the differences below.
Posts
- Think of these as news articles which are to be updated on a regular basis
- Listed in reverse chronological order
- You can sticky posts which will place them at the top of the list
- You add categories and tags to posts to help with sorting and searching
Pages
- Static and not listed by date
- Basic content type for your website that is not updated often