Hi

I will take these in reverse order!

3. Post type archive. In the theme, you have to place the search form using a widget area, by using the provided shortcode or search form widget. That assumes your theme gives you such a widget area. Failing that, you have have to manually edit the template.php for the page in question and add the shortcode using the wordPress do_shortcode function.
2. As an archive is the more complex and does require you to understand where and how to edit the theme’s files. Not easy if you do not know how.
1. As with 3, you still have to place the search shortcode on the page, but this method uses a template from within Search & Filter’s template folder, called results.php. You can copy this to your child theme folder (the instructions are on the documentation page) and the file is deliberately made less complex to allow easy editing, usually by cut and pasting the bits to where you want them, or removing bits, and the add HTML classes and id’s and other HTML structure so that the page matches what you see on a normal page in your theme.