HTML forms are used to collect user input on web pages. The <form> element defines an HTML form, which contains various form elements like text fields, checkboxes, radio buttons, and submit buttons to collect input from the user. Forms submit data using the GET or POST methods, with POST being more secure as it does not display submitted data in the URL. Common form elements include <input>, <select>, <textarea> to collect different types of user input like text, selections, and multi-line text. Forms are an essential part of creating interactive web pages that collect and process user data.