Add custom hook(filter and action)

Hello All,

How to add custom hook in WordPress?
Here what I’ve tried before,

# add action in functions.php

add_action('my_logo', 'my_logo');

function my_logo($logo)
{
	echo $logo;
}

# do action in template file

$logo = '<img src="PATH"/>';
do_action('my_logo', $logo);

Now I want my logo wrapped by adding filter to my_logo,

add_filter('my_logo', 'modified_logo');

function modified_logo($logo)
{
	$logo = '<span>'.$logo.'</span>';
	return $logo;
}

But not getting expected result.
Any help appreciated.