Yes. You can connect several accounts of the same kind — a work Google account alongside a personal Outlook one, or two Google accounts. Mail from every account arrives in the one unified inbox (each row shows which account received it), and every calendar appears in the one week view, colour-coded per account with a legend to show or hide each one.
One account of each type is the default: new mail is sent from it and new events are created on it, unless you name another account at the time. Replies always go out from the account that received the original message. Set the default in Settings → Connections, or just ask Nell.
How many accounts you can connect depends on your plan — see pricing for the limits.