Split
Household groups — the people you live with, fixed bills, month after month — and trip groups — temporary, many expenses in a few days, settled at the end.
You join a group with a six-letter code, never by email. You can add someone by name alone, before they have the app; they claim that spot when they join with the code.
Month
Your personal budget: what comes in, what goes out, categories, accounts and recurring rules.
The contents are private: your entries, categories and amounts stay on your iPhone and sync through your own iCloud. They are not shared with anyone.
Profile
Apple account, the name other people see in the group, language, theme, Face ID lock, alerts and usage data sharing.
Deleting your account is here too, without having to ask anyone.