Under Account, the Profile page holds your name, company, address and phone - the details that appear on your invoices. Keep the email address current above all: invoices, ticket replies and renewal notices go there, and a dead address is how domains expire unnoticed.
The Contacts page adds more people to the account - a colleague, your developer, your accountant. Each contact has their own name and email. Use it instead of sharing your own password: sharing the password shares everything, including the right to close the account.