These path settings are important for proper linking within MantisBT. In most scenarios the default values should work fine, and you should not need to override them.
URL to your installation as seen from the web browser; this is what you type into the URL field. Requires trailing '/' character. eg. 'http://www.example.com/mantisbt/'. In the following example https protocol is used: eg. 'https://www.example.com/mantisbt/'. MantisBT will default this to the correct value. However, in some cases it might be necessary to override the default. This is typically needed when an installation can be accessed by multiple URLs (internal vs external).
This is the URL to the icons (images) directory as seen from the web browser. All MantisBT images/icons are loaded from this URL. The default value for this URL is based on $g_path (i.e. '%path%images/'). Note that a trailing '/' is required.
Short web path without the domain name. This requires the trailing '/'.
This is the absolute file system path to the MantisBT installation, it is defaulted to the directory where config_defaults_inc.php resides. Requires trailing '/' character (eg. '/usr/apache/htdocs/mantisbt/').
This is the path to the core directory of your installation. The default value is usually OK, unless you move the 'core' directory out of your webroot. Requires trailing DIRECTORY_SEPARATOR. character.
This is the path to the classes directory which is a sub-directory of core by default. The default value is typically OK. Requires trailing DIRECTORY_SEPARATOR. character.
This is the url to the MantisBT online manual. Requires trailing '/' character.