Cookies are small text files that are stored on your computer's browser when you visit a website. These cookies keep track of your movements on the site to help you pickup where you left off, and remember your login as you use the site.
Most browsers have the option of either accepting all cookies, showing an alert before accepting a cookie, or not accepting cookies at all. You need to have cookies enabled to use Ministry Sync.
You can enable your browser's cookies in most browsers by going to Settings > Advanced (Options) > Privacy Settings. This article has more information on specific browser settings.