At the heart of CSS is the Style Declaration.

1. Selector: the selector is used to 'select' the HTML element that you want to style.
2. Declaration Block: is everything between the curly brackets.
The Declaration Block is further broken down into:
1. CSS Property
2. Value
For instance, the Style Declaration (Style) in the image above means all paragraphs will have a font-size of 14px.
The letter 'p' is a Tag or Element Selector. This type of Selector simply selects an HTML tag by indicating the letters of the HTML tag.
For instance, the paragraph tag is written as such - <p>
Therefore, we just use the letter 'p' to select 'paragraphs'.