If this issue getting you have to increase  max_allowed_packet in MySQL ini file

xampp –> mysql –> my.ini

max_allowed_packet = 1M –> max_allowed_packet = 16M

1. You will create two files header.php and footer.php.
2. Create a folder “include” in your theme directory.
3. Suppose that your theme directory is “aviweb” sites/all/themes/aviweb. Put header.php and footer.php file in “sites/all/themes/aviweb/include” theme folder.
4. By using html and php you can write code in header.php and footer.php.
5. Now you can include both files in page.tpl.php in header area and footer area like PHP.

<?php include_once($theme_path.’/include/header.php’); ?>

<?php include_once($theme_path.’/include/footer.php’); ?>

1. Make a backup of your Drupal instance (database).
2. Set your site on maintenance mode.(Click here)
3. Delete all the files & folders inside your original Drupal instance except for /sites and its sub-folders.
4. Warning: If your Drupal installation is built from a distribution your site will break if you delete the /profiles folder. Don’t delete the profile folder that corresponds to the distribution you installed, for example /profiles/kickstart if you installed Drupal Commerce Kickstart.
5. Copy all the folders and files except /sites from inside the extracted Drupal package [tar ball or zip package] into your original Drupal instance location.
6. Some updates do not include changes to setting.php and some do. If the update release includes changes to settings.php you will need to replace your old settings.php in …/sites/default/ with the new one, and then edit the site-specific entries (eg database name, user, and password) in the setting file.
7. If you have modified files such as .htaccess or robots.txt re-apply those changes to the new files.
8. If you have a favicon.ico file that was deleted replace it too
9. Login to your site as administrator
10. Run “update.php” by navigating to http://yourdrupalsitename/update.php and follow the process to update your Drupal instance
11. Disable maintenance mode.

To create front page template please find below steps

• Create “page–front.tpl.php” template in current theme and copy the home page PHP code into that.
• Next create one “Home” page and Promote as front page like below screenshot.

• Once we done above steps it will work as front page with “page–front.tpl.php” code.

Please find below given clear explanation…..

• To me, the concept of “node” is fairly clear: It is an “instantiation” of a content-type. When you add content, you choose the type, e.g. “Article”, and the content that you add (e.g. the article text, title, images, etc.) is stored as one unit in the database, and is also often assigned its own URL path. A node is then retrieved, upon user request (i.e. the appropriate HTTP GET), by the node module and passed on to the template which places in on its appropriate place in the layout and generates and returns the webpage (the actual final markup that is served to the browser) by adding in other components of the page (e.g. menus, blocks, etc.). What I find a bit fuzzy however is the concept of entity. A user is an entity, so is a node? How about a role, or a block? How about a comment or a menu? Are those entities too?I can’t yet quite see its place in the overall scheme.
• To me, “entity” is just a fancy synonym for “thingie”, which is about as vague (or general/abstract) as you could get. Indeed, if knew what is NOT an entity, it might become clearer.

/* Menu code for drupal 7 */
<?php
$main_menu_tree = menu_tree(‘main-menu’);
foreach ($main_menu_tree as $key => &$main_menu_item) {
if (is_numeric($key)) {
$main_menu_item[‘#below’][‘#theme_wrappers’][0] = ‘some_other_theme_wrapper’;
}
}
print drupal_render($main_menu_tree);
?>

Please find below to clrear cache in Drupal.

1. The easiest way to clear the Drupal cache is to go to Administration > Configuration > Development > Performance
(http://example.com/admin/config/development/performance)
2. Click the button “Clear all caches”

The most convenient way to rebuild Drupal’s cache is by using Drush.

Drupal 8:
drush cache-rebuild

Drupal 7 and earlier:
drush cache-clear all