Showing User Information

/**
 * Get an object that contains the current user's info:
 */
$current_user_obj = wp_get_current_user();

/**
 * Print out the object so that you can see its contents:
 * (Note: this is just for debug/dev, don't use on live site)
 */
echo '<pre>'; print_r( $current_user_obj ); echo '</pre>';

/**
 * Now that you know what the object contains you can
 * get and use the data in your project like this:
 */
echo $current_user_obj->data->display_name;

Be careful not to expose sensitive user info like passwords, login info, etc.

See these links for more info:

http://codex.wordpress.org/Function_Reference/wp_get_current_user
http://codex.wordpress.org/get_currentuserinfo
https://developer.wordpress.org/reference/functions/get_currentuserinfo/