Menus, sidebars and widget

Hello,
I am new to wordpress
From the ebooks, I learn that I should code inside functions.php to create new menus, why should I do that If I am able to create menus from the admin section
sidebar.php sidebar-right.php
I read that I place some function like get_sidbar() or get_sidebar(‘right’); to get sidebar.php or sidebar-right.php
is this the way to do it, but inside sidebar-right.php, how to call a specific sidebar created
These things confuse me