now I will cover the mymodule.module part

there is three hooks we use alot in backend those are

insert_hook, update_hook, delete_hook

each hook add node, delete node, and update node

insert_hook

starting clear we can implement hook insert by name modulename_insert

function modulename_insert($node) {
  db_query("INSERT INTO {mytable} (nid, extra)
    VALUES (%d, '%s')", $node->nid, $node->extra);
}


function modulename_update($node) {
//if the node is set for revision insert instead of delete
if ($node->revision) {
 modulename_insert($node);
 }
 else
{
 db_query("UPDATE {mytable} SET extra = '%s' WHERE nid = %d",
    $node->extra, $node->nid);
}
}

function modulename_delete(&$node) {
  db_query('DELETE FROM {mytable} WHERE nid = %d', $node->nid);
}