I need to get a brief description with appropriate syntax of checkboxes,alertboxes in form feed in HTML???

Answer 1

visit w3school input tags section

Answer 2

Check boxes are form elements, but alert boxes doesn't ^^
What do you mean by "alertboxes"?

Check boxes:
<input type="checkbox">

For other's attributes:
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/checkbox
http://www.w3schools.com/jsref/dom_obj_checkbox.asp
http://www.w3schools.com/html/tryit.asp?filename=tryhtml_checkbox