Difference between <input type='button' /> and <input type='submit' />

<input type="button" /> buttons will not submit a form - they don't do anything by default. They're generally used in conjunction with JavaScript as part of an AJAX application.

<input type="submit"> buttons will submit the form they are in when the user clicks on them, unless you specify otherwise with JavaScript.

The first submit button of the form is also the one being clicked for implicit submission, f.e. by pressing enter in a text input.

A 'button' is just that, a button, to which you can add additional functionality using Javascript. A 'submit' input type has the default functionality of submitting the form it's placed in (though, of course, you can still add additional functionality using Javascript).