Profile and security

Account details
The company name, tax number, website and contact email. These are the business details; the ones that go on the invoice are set in Subscription.
Password
Changed from here, entering the current one and the new one twice.
Two-step verification
Recommended, and much more so if more than one person logs into the panel. You turn it on with an authenticator app (Google Authenticator, 1Password, Authy...): you scan the code and from then on, as well as the password, it asks for a six-digit number.
Your guests' phone numbers are in this panel. If somebody got into your email, two-step verification is the only thing that would stop them getting in here too.
Language
The selector top right switches the panel between Catalan, Spanish and English. It's per person, not per restaurant: everyone can have it however they like.