There is no denying filters in WordPress are amazing but for me the syntax always seems backwards (im not saying its wrong just how my mind reads it), so i thought i would write an article to make it clear (for me anyway).
apply_filters()
Adds a event in the php exacution that you can hook into useing the add_filter() function.
This wrapps what you want to be able to filter(change).
mixed apply_filters ( string $event_name, mixed $value, mixed $... );
add_filter()
Adds a filter to the event that is set by apply_filter() function.
This is the change you want to make to the filter.
bool add_filter ( string $event_name, callable $callback_name, integer $priority = 10, integer $number_of_args = 1 );