The purpose of progress bars is showing the progress of a task or action to the users. Bootstrap provides several types of progress bars. Note: Progress bars are not supported in Internet Explorer 9 and earlier (because they use CSS3 transitions and animations to achieve some of their effects).
A modal is a child window that pop up over parent window. The purpose is to display content from a separate source without leaving the parent window. In case to make Modal Plugin work properly you will need bootstrap.js or bootstrap.min.js.
Bootstrap provides different styles of buttons. You can use any of the available button classes to quickly create a styled button. As a best practice, Bootstrap highly recommend using the <button> element whenever possible to ensure matching cross-browser rendering.
All HTML headings, <h1> through <h6>, are available. .h1 through .h6 classes are also available, for when you want to match the font styling of a heading but still want your text to be displayed inline.