BuddyPress.org

You need to compare the theme you want to use and one of it’s files i.e page.php or index.php to one of the newly created BP ones like /member/index.php the BP files need to mirror the html markup and class/ID’s structure that your chosen theme files have e.g if your theme file has an element named ‘content-main’ and the BP file has ‘content’ then the BP one needs to change to match.

I’m afraid that if it’s still ‘all gibberish’ then things will be difficult, adjusting a theme to work with BP does require a degree of coding knowledge albeit at a basic level you must be comfortable modifying files and working with HTML markup.