In CSS, selectors are used to select the HTML elements that you want to style. For example: p tags, anchors, h1s.
Properties are what you are specifically trying to set. It can be the color, width, border, etc.
The :hover selector is used to select elements when you mouse over them. (:hover).
The :visited selector is used to select visited links. (:visited).
The background-color property in CSS allows you to apply a solid color as a background on an element.
The font-family property allows you to change the initial font that is currently on your page to a
specific font. It is recommended to have a generic family listed to ensure the best typographic experience. The browser will default to a monospace font if the user's system doesn't allow the value listed.
In conclusion, selectors are able to tell the browser what to select in order to style the elements that you want.
Properties are a characteristic whose associated value defines one aspect of how the browser should display the element.
Example:
h1 (selector ) {
color (property): blue; (value)
}