When signing up, you'll have to provide a login and email. Your login name will be displayed on the website with decks/replays/... you create. Your email will never be shared with anyone and won't ever be used to send anything you didn't opt-in for (like password resets or notifications you enable, should extra features be added). IP addresses of logged in users are also recorded, to be able to deal with potential abuse of website's tools.
Cookies are also used by the statistics system and may contain information about your machine/browser. These informations are never shared with a third party, analyzed to display targeted ads or track your visiting habits or anything else that isn't harmless. If you want to opt out of these, you can do so by clicking here. Note that this will place a "Don't track me" cookie on you browser to remember to not track any information during your future visits.
Advertisements displayed on the website might place their own cookies. If you do not want these, browser extensions such as Adblock and NoScript are recommended to be able to disable them globally.