How do I add a category of my own?

In an expense, tap Category. The group's own categories come first, under the group's name, then the built-in ones, grouped by their colour: food and drink, travel and transport, home and bills, fun and shopping, and everything else.

Tap New category, give it a name, choose one of the five colours and a symbol, and tap Add category. The expense is filed under it, and everyone in the group can use it from then on. A name the group already uses is refused, so the charts never show two categories called the same. A group can have up to 30 categories of its own, archived ones included.

Anyone in the group can add a category. The person who added one, and the group's owners and admins, can rename it, change its colour or symbol, or archive it: open the group, tap the gear for Group settings, then Categories.

An archived category leaves the list when you add an expense, and keeps its past expenses, in the group's totals and charts too. Bring back puts it back in the list.

The CSV export writes a group's own category by its name. When you import a group, a category Evensies has no built-in for comes across as one of the group's own.