If you are new to programming with HTML, CSS, and JavaScript (or just need brushing up), we recommend you start with the following tutorials on Codecademy. We will reiterate some key concepts briefly in the Foundations module, but these tutorials provide an excellent skill base. Each of these are available with a free-tier account at https://codecademy.com.
{% embed url="https://www.codecademy.com/learn/learn-html/modules/learn-html-elements" %}
{% embed url="https://www.codecademy.com/learn/learn-css" %}
{% embed url="https://www.codecademy.com/learn/introduction-to-javascript" %}