At Admin Panel -> Settings -> System Configuration -> "Cookie Details", you have a set of options for configuring cookies. Cookies are small files stored on the visitor's computer (including yours) which contain the login information (so that users can stay logged in across multiple pages) and other small bits of data like recently viewed listings and pages.
Important note: When you change cookie details, you may encounter cookie conflicts where previously set cookies from the former details conflict with the new cookies. If you find yourself having login or logout issues after changing cookie details, clear cookies in your browser.
The first option is the cookie path. If this field is blank, cookies are only accessible from the directory they're set in. This would be bad because URL-rewriten pages that appear as subdirectories would log people out, and moving between the front end and admin panel would log you out. So, the value should normally be / -- the slash means that the cookie will be accessible from any subdirectory or the top level. If you have several WSN scripts installed which you've not integrated the membership of for some reason, you would have to set /subdirectory/ as the path (change "subdirectory" to the name of the actual subdirectory the copy of WSN is installed to) so that the two separate script logins don't conflict with each other.
The next field is the cookie domain. If you don't use subdomains, you can leave this blank. If you do use subdomains and want to integrate with scripts on other subdomains, or you use WSN's categories as subdomains URL rewriting option, then you'll need to type .yourdomain.com as the cookie domain. Notice the leading dot. This will tell it to set the cookies across all subdomains of yourdomain.com.
The default duration field controls how long most cookies last. (Exceptions are voting cookies and link hits cookies for which the expiration times are specified at Admin -> Listings -> Listing Settings.) For example, this will control how long you remain logged in after you login. If this value were set to 86400, then you would be forced to login again once every day (there are 86400 seconds in a day). Members can override this by editing their profile, or you can override it in the registration defaults as well.
Next, you can set a privacy policy. Cookie privacy policies allow the user to click a spot in their browser (lower right in MSIE) to see how you're using their info. This is basically useless, but Internet Explorer 6's default security settings require that cookies must have a privacy policy. Thus in order to make sure your users can login you'll need something in this field. Fortunately, IE 6 doesn't actually check to see that the policy is valid... only that there is a URL. Thus, you can leave a dummy URL there like www.somesite.com/w3c/p3p.xml and it will serve the purpose of ensuring that all your Internet Explorer users can login.
Finally you can change the cookie names. This is useful if you want to have multiple WSN installs sharing the same cookie path without integrating their member systems.