Bootstrap is an open source HTML, CSS, and JS library that helps you build websites and apps very easily. It is a library of components that you can reuse instead of re-creating every component over and over again. Bootstrap is responsive and mobile first; this is essentially what Bootstrap is all about, and why it has become so popular with web developers. Now, let's say the developers are creating different versions of their website for different devices; just by applying small amounts of code to the pages, the sites will be displayed correctly on any device, which saves time and additional cost.

There are major updates every couple of years. Bootstrap 2 was officially released in 2012, then was reasonably quickly replaced with Bootstrap 3, which was released in 2013. Then, of course, there came Bootstrap 4 in 2016. The more stable it becomes, the longer the gaps between the releases. Hopefully, it won't be too long before Bootstrap 5 arrives. 

Bootstrap 4 is still very new, so a lot of developers are still using Bootstrap 3:

Within the framework, there are also a large number of elements and components that you can use within your sites or pages. Everything in the Documentation tab will be essential; it contains invaluable information that you can refer back to, and is where you want to go to learn about new elements or components:

It starts with the introduction to Bootstrap and includes all the information you need to get started. Then, on the left-hand side, it provides all the sections and components. This is probably one of the most popular sections you will view as it contains all the different elements you can use within Bootstrap. So, essentially, this can help you build your pages.

There are also some examples or quick start examples that Bootstrap provides in the Examples tab. These are ideas for practicing or testing things out after you've completed this chapter, so you can put your new ideas into your own page and test out what you've learned throughout the chapter:

It's worth bookmarking this page or coming back here in the future. Now, another essential section to keep an eye on is the Bootstrap blog; this is where all the updates are posted, no matter how big or small. So, it's ideal to keep an eye on it just in case some changes occur that may have an effect on your site.

So, in a nutshell, that's just a quick overview of the Bootstrap site. It's worth bookmarking the components page so you can quickly refer back to it in the future if you need to. Next, we're going to take a closer look at what those components are, and how we are going to use them.