Missing the MySQL extension

Please help! I am very inexperienced at this but used to be able to update my website and now I cannot log in to do anything. The error “Your PHP installation appears to be missing the MySQL extension which is required by WordPress.” continues to come up and I cannot access anything, even updating the WP software. Can anyone help walk me through this simply….everything I find on google is too complex for me. Thank you in advance.

The page I need help with: [log in to see the link]