If all you want to do with your website is to display some basic text and images, then HTML and CSS are enough to do the job.
However, if you want to do more — such as change styles dynamically, animate menus, create functional buttons, validate data entered into a form, and much more — you're going to need another tool.
Unlike jQuery and Bootstrap, which are can be used to accomplish just about anything, Modernizr is a niche script used for a very specific purpose: to tailor a website visitors experience based on the features supported by the visitor's browser.
Also see our introduction to Node.js
Free Interactive Courses
Code School is a premium (paid) education provider.
The jQuery Foundation, in cooperation with Code School, has pulled together an introductory interactive jQuery course.
Online Books and Tutorials
Written for cats, but also suitable for their human companions, this tutorial won't turn you into a full-fledged developer, but it covers the basics and will help you develop a solid foundation to build on.
The content provided by MDN is extremely detailed and is considered adequate to get a disciplined student all the way from beginner status to being a competent front-end developer.
The You Don't Know JS books series, by Kyle Simpson, is a deep-dive series that aims to help you develop mastery of each topic covered.