domain.com/webmail
U: user@domain
P: 654123qweytr
From there you should see an icon that says: “Change Password”. You can use it to change password for your mailbox.
To start using your emails just click on Squirrel Mail or Horde.
By the way, you could also configure your Outlook program or any other one to work with this.
Let us know if you need help with that.