how to make a html button do something code example

Example 1: button functions html

<script>
 function myFunction() {
   alert("ALERT");
 }
</script>
<button onclick="myFunction">Click</button>

Example 2: html button action

A form with two submit buttons. The first submit button submits the form data to "submit_data.php", and the second submits to "send_data.php":

<form action="/submit_data.php" method="get">
  <label>Name:</label>
  <input type="text" id="uname" name="uname"><br><br>
  <label>Age:</label>
  <input type="text" id="uage" name="uage"><br><br>
  <label>Address:</label>
  <input type="text" id="uaddress" name="uaddress"><br><br>
  <button type="submit">Submit</button>
  <button type="submit" formaction="/send_data.php">Submit to another page</button>
</form>