Permalinks are customized URL structures you can create to substitute for the machine generated URLs created by WordPress. This allows you to develop aliased URLs that are more reader and search engine friendly. The Permalink Settings group contains the following items:

Common Settings: provides five different formats to use for URL creation

Default: creates no alias

Day and Name: creates year, month, and day format with name of post

Month and Name: creates year and moth format with name of post

Numeric: auto-numbers post and uses number for URL alias format

Custom Structure: defined by you, if desired

Optional Settings: allows creation of custom URL structures for Categories and Tags