You can download the current stable version, Coq 8.12.0, released in July 2020. It features many quality-of-life improvements, including goal differences as well as numeral and custom notations.

To use Coq, you will need a user interface. Many editor support extensions are available (for Emacs, Vim, VSCode, etc.), as well as CoqIDE, a standalone IDE for Coq. The User interfaces page provides a full list, with more details. If you are only looking for a quick way to try Coq without installing anything, we recommend you use jsCoq.