One cookie is set to try to remember your name (not your password) for 28 days if you check the 'remember me' checkbox when signing in.
The other cookie is a 'session' cookie.
This cookie contains a unique number which is an index into some data on our servers which – if you're logged in – holds your sign in details. This information is used to remember you from page to page. When you sign out of skignz, or leave skignz for approximately 24 minutes, the 'session' cookie is destroyed.
There's more about cookies at http://www.aboutcookies.org