Three cookies are used on this site.
The essential one is the session cookie, usually called "MoodleSession". You must allow this cookie in your browser to provide continuity and to remain logged in when browsing the site. When you log out or close the browser, this cookie is destroyed.
Another cookie is called "EU_COOKIE_LAW_CONSENT." This cookie stores your acceptance of the privacy policy, which you will be prompted for in a banner in the footer at the beginning of your session. If you set this cookie, then it is valid for a maximum of one month and the banner will not be displayed again on further page views. The set cookie can be deleted at any time manually or, if you have configured your browser accordingly, automatically when you close the web browser.
The third cookie is purely for convenience, usually called "MOODLEID1_" or similar. It just remembers your username in the browser. This means that when you return to this site, the username field on the login page is already filled in for you. It is safe to refuse this cookie - you will just have to retype your username each time you log in.