types of hooks in WordPress...

Hooks allow user to create WordPress theme or plugin with shortcode without changing the original core files.

two types of hooks:

1) Action hooks 2) Filter hooks 1. Action hooks : Action hooks allow you to insert an additional code from an outside resource. For Example: Go to the Link CLICK HERE. You can see action hook example used for redirection for custom login page. 2. Filter hooks Filter hooks will only allow you to add a content or text at the end of the post. For example: We want to change the Excerpt length. then we have to use the Filter Hook

function custom_excerpt_length($length) {
    return 200;
}
add_filter('excerpt_length', 'custom_excerpt_length');