If your sidebar is in a theme file called “get_sidebar()”, as it should be for ease-of-use, just add this tag to your single.php, index.php, category/search &c&c:
<?php get_sidebar(); ?>
If there isn’t a sidebar.php file, make one in your favorite text editor and save it as sidebar.php.
N.B. If you name it anything else, sidebr.php, thesidebar.php, dancing_bears.php, &c, the WordPress tag get_sidebar won’t work. You’ll need to use an “include” function at that point.
Save yourself the hassle; name it sidebar.
Cheers!