<!DOCTYPE html>
<html>
<body>
<h1 onclick="this.innerHTML = 'You clicked'">Click on this text</h1>
</body>
</html>

In the following example, the onclick event calls a function ‘changetheText’.
<!DOCTYPE html>
<html>
<body>
<h1 onclick="changetheText(this)">Click on this text</h1>
<script>
function changetheText(id) {
id.innerHTML = "You clicked";
}
</script>
</body>
</html>

The (this) word above allows the function to identify which text the function is being called from. Check out the following code:
<!DOCTYPE html>
<html>
<body>
<h1 onclick="changetheText(this)">Click on this text</h1>
<h1 onclick="changetheText(this)">Click on this text as well</h1>
<script>
function changetheText(id) {
id.innerHTML = "You clicked";
}
</script>
</body>
</html>
