There are two main types of modifications for b2evolution: plugins and hacks.

Plugins are the easiest to install. They usually involve dropping a file into your plugins directory and then installing it through the backoffice. Plugins first appear in the Phoenix version of b2evolution. Read more at the b2evolution Manual.

Hacks are modifications that you manually make. The hack author generally gives detailed instructions for which files to edit and what, exactly, you need to add or change. If a hack involves editing a core file (anything outside of the plugins, conf and skin directories), then you are responisble for backing up your files before you change them. If you attempt a hack and it breaks your blog, then you can restore the file from your backup. Neither the hack author, nor anyone invloved with b2evolution is responsible for any damage to your site that results from you editing a core file. Even if you successfully implement a hack, it will usually be lost when you upgrade your b2evolution software.