What button types to use and when Bootstrap 3?

Question

css

There are 4 main types of buttons using Twitter Bootstrap 3.
Which ones should be used and when? ??

1 - Ссылкой:
<a href="" class="btn btn-success btn-lg" role="button" > Button by ' a '</a>
2 - Кнопкой:
<button class="btn btn-primary" type="submit"> Button by ' button '</button>
3 - Инпутом:
<input type="button" class="btn btn-danger btn-sm" value="Button by ' input '">
4 - Инпутом :
<input type="submit" class="btn btn-info btn-xs" value="Button by ' input + submit '">

Answer 1

Normal html semantics.
a- a link, a transition to another document
button- a ui element for some action on click (add to cart for example)
button[type=submit], input[type=submit]- submitting a form
The difference between input and button in this case is the impossibility to nest elements inside or use after/before pseudo-elements.
Bootstrap is just a set of css styles, not some other universe.