add meta key or meta value or custom field for post

// Post offer box
add_action( 'add_meta_boxes', 'post_offer' );
function post_offer() {
   add_meta_box(
       'post_offer',
       __( 'Price', 'agrg' ),
       'post_offer_content',
       'post',
       'side',
       'high'
   );
}

function post_offer_content( $post ) {
wp_nonce_field( 'myplugin_meta_boxeee', 'myplugin_meta_box_nonceeee' );
$post_offer = get_post_meta( $post->ID, 'post_offer', true );

echo '<label for="post_offer"></label>';
echo '<input type="text" id="post_offer" name="post_offer" placeholder="'._e('Enter price here','agrg').'" value="';
echo $post_offer;
echo '">';

}

add_action( 'save_post', 'post_offer_save' );
function post_offer_save( $post_id ) {

global $post_offer;

if ( ! isset( $_POST['myplugin_meta_box_nonceeee'] ) ) {
return;
}
if ( ! wp_verify_nonce( $_POST['myplugin_meta_box_nonceeee'], 'myplugin_meta_boxeee' ) ) {
return;
}
if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
return;
}

if(isset($_POST["post_offer"]))
$post_offer = $_POST['post_offer'];
update_post_meta( $post_id, 'post_offer', $post_offer );

}

add custom fields user registration wordpress

http://blog.ashfame.com/2010/11/add-custom-field-registration-wordpress/



<?php
/*
Plugin Name: Custom Profile field as a Registration Field
Plugin URI: http://blog.ashfame.com/2010/11/add-custom-field-registration-wordpress/
Description: Sample plugin for adding a custom profile field to WordPress and on the registration page
Author: Ashfame
Version: 0.1
Author URI: http://blog.ashfame.com/
*/

/**
 * Add additional custom field
 */

add_action ( 'show_user_profile', 'my_show_extra_profile_fields' );
add_action ( 'edit_user_profile', 'my_show_extra_profile_fields' );

function my_show_extra_profile_fields ( $user )
{
?>
<h3>Store information</h3>
<table class="form-table">
<tr>
<th><label for="twitter">Twitter</label></th>
<td>
<input type="text" name="twitter" id="twitter" value="<?php echo esc_attr( get_the_author_meta( 'twitter', $user->ID ) ); ?>" class="regular-text" /><br />
<span class="description">Please enter your Twitter username.</span>
</td>
</tr>
<tr>
<th><label for="sname">Store Name</label></th>
<td>
<input type="text" name="sname" id="sname" value="<?php echo esc_attr( get_the_author_meta( 'sname', $user->ID ) ); ?>" class="regular-text" /><br />
<span class="description">Please enter your Store name.</span>
</td>
</tr>
</table>
<?php
}

add_action ( 'personal_options_update', 'my_save_extra_profile_fields' );
add_action ( 'edit_user_profile_update', 'my_save_extra_profile_fields' );

function my_save_extra_profile_fields( $user_id )
{
if ( !current_user_can( 'edit_user', $user_id ) )
return false;
/* Copy and paste this line for additional fields. Make sure to change 'twitter' to the field ID. */
update_usermeta( $user_id, 'twitter', $_POST['twitter'] );
update_usermeta( $user_id, 'sname', $_POST['sname'] );
}

/**
 * Add cutom field to registration form
 */

add_action('register_form','show_first_name_field');
add_action('register_post','check_fields',10,3);
add_action('user_register', 'register_extra_fields');

function show_first_name_field()
{
?>
<p>
<label>Twitter<br/>
<input id="twitter" type="text" tabindex="30" size="25" value="<?php echo $_POST['twitter']; ?>" name="twitter" />
</label>
</p>
<p>
<label>Store Name<br/>
<input id="sname" type="text" tabindex="30" size="25" value="<?php echo $_POST['sname']; ?>" name="sname" />
</label>
</p>
<?php
}

function check_fields ( $login, $email, $errors )
{
global $twitter;
if ( $_POST['twitter'] == '' )
{
$errors->add( 'empty_realname', "<strong>ERROR</strong>: Please Enter your twitter handle" );
}
else
{
$twitter = $_POST['twitter'];
}

global $sname;
if ( $_POST['sname'] == '' )
{
$errors->add( 'empty_realname', "<strong>ERROR</strong>: Please Enter your Store name" );
}
else
{
$sname = $_POST['sname'];
}
}

function register_extra_fields ( $user_id, $password = "", $meta = array() )
{
update_user_meta( $user_id, 'twitter', $_POST['twitter'] );
update_user_meta( $user_id, 'twitter', $_POST['sname'] );
}

?>