Use the ‘Button’ element. The Bootstrap class for a button is simply .btn. That leaves the button unstyled. The extra classes, such as e.g.
In other words, all the names written as the button text in the examples, are for the look of the button. If you want to use other colours, shapes and sizes, you need to take off those classes and give them a class of your own that you can style yourself.
If you want larger or smaller buttons, there are also the classes
The differences are just in the font size and the padding.