(in WordPress)I am wondering where to edit the BP templates - should I edit the core template files(in wp-content/plugins/buddypress) or is there a way to somehow make your own BuddyPress theme ?
Thanks.
Start by adding a Child Theme if you haven't done so already.
Read the Template Hierarchy link like slaFFik suggested.
Add a directory 'buddypress' to your child theme.
Copy the core template files you want to edit from wp-content/plugins/buddypress/bp-templates/bp-legacy/buddypress/(XXX/YYY/)zzz.php into themes/yourchildtheme/buddypress/(XXX/YYY/)zzz.php
If you edit the core files directly your changes could be lost when you update BP.