First and last name — your name on your account.
Email — your identity. It can't be changed here; contact support if it needs to move.
Timezone — filled in from your device the first time you use the app. It sets when your reminders arrive and what "today" means for them; without one they run on UTC. If it's wrong, pick yours and press Save changes.
Theme — Dark (default) or Light, saved on this browser. The support chat follows the same choice.
The name other members of a shared space see, and the name your assistants see, is the one your account was created with: your name from Google or Microsoft, or the part of your email address before the @. Changing your first or last name here doesn't change it.
Further down the page is Two-step sign-in (see Sign-in options and the email code). The Reminders tab turns reminders and the reminder email on or off and sets the hour they arrive. The Email forwarding, Billing and Referrals tabs are covered in their own articles.