CSS, or Cascading Style Sheets, is a styling language used to describe the presentation of a document written in a markup language. It is used to control the layout and display of elements on a web page.

To start learning CSS, you can take a look at the official CSS documentation on the W3C website, which provides a comprehensive overview of the language and its features. Additionally, there are many online tutorials and resources available to help you learn, such as Codecademy, W3Schools, and freeCodeCamp.

As for best practices, here are a few things to keep in mind as you learn CSS:

Keep your CSS organized and easy to read by using comments and naming conventions.

Use a CSS preprocessor such as Sass or Less to make your CSS more maintainable and efficient.

Use a CSS reset or normalize file to ensure consistency across different browsers.

Use CSS selectors carefully to avoid making your styles too specific and hard to override.

Use CSS Grid and Flexbox for layout, instead of using tables or floats.

And always keep in mind to test your code on different browsers and devices.