Posts
The Posts Menu
Posts are like a page with a few differences. 
They can be used to create a long scrollable blogroll, like joined pages.
For a business website I prefer the posts to be used for articles only and the “PAGES” to be the traditional 1 page per article or content type. Business website . . . . head to the Pages menu to create your pages.
The “Posts” is a list of all your current posts/articles and where you click one of them to edit it.
“Add New” is where you add a new post/article.
The tags and categories are for posts to join together similar type content. Both can be made before creating a post by clicking the tags or categories button or at the time of writing your post by adding them in an area on the right side. That area is also where you assign your tags and categories that are already made.
Each post can have a particular category it is assigned to and/or tags assigned to it.
Categories:
For an example you may have a tourism website, so your categories can be Sightseeing, Adventures, Accommodation. In turn each of these can have a sub-category like areas, Auckland, Wellington etc.
Tags:
Normally your published post would have underneath it the tags you have assigned and each tag is clickable to then return all of your posts that have that same tag assigned to them. Tags can have the above examples as tags instead of categories.
In the above case a post about Wellington Accommodation would have at least two tags assigned, Wellington and Accommodation and your article or post could be found by clicking either of those tags beneath another article that shares a common tag and be returned within the blogroll of that tag.
Both Categories and Tags can be useful. Categories have built in WordPress functions which can add a clickable menu into a sidebar to return all posts in a given category.
The Tags benefit is being underneath an article that can then be clicked on for returning common articles.
Other relevant content to be read in conjunction:
In Settings/General, assign which type of content . . . post or page is the main front page to your website.
Care with comments, they can be abused with Porn Links.
