You can access your email accounts in a browser:
type /webmail after your domain name
A login box should shortly appear.
You may get a choice of connection type although this often happens automatically.
Sometimes the local network/connection/security software will prevent the connection due to tight security settings. The only way to fix this is to change these.
ID is full address
Password for that email address
A short delay is usual then a choice of webmail programs appears.
Horde is slightly faster with no as many extra features.
Pick one and do the normal webmail thing.
When you read webmail, the messages stay on the server. If you are not reading your email with an email client eg Windows Mail, your mailbox can fill up.
If you delete emails on webmail, you must also Purge Deleted to remove it form the server.
It is unadvisable to use a public computer where emails may have some sensitive data such as your credit card number.
Be sure to logout of the webmail