Add somebody

Open Workspace › People and Access and press Add somebody.
Enter their Email and, if you like, Name (optional).
Choose a Role (see Roles and permissions).
Under How they get in, choose Send them an invitation link — they accept and sign in with their own account — or Create the account now and give them a password.
Save.

Seats shows how many of the company's seats are used. A login is a seat; an employee on payroll is not.

Adjust one person's access

Open a person. Change their Role if needed.
For any single permission, choose grant to add it or deny to remove it, on top of the role. Add and remove Marketplace plugins cannot be granted: it comes with the Owner and Administrator roles only.
To give temporary access — an external auditor, for example — enter the number of Days after which it ends.
Save.

On Users, press Add someone outside. Add someone outside the company opens.
Enter their Email, Name and Who they are with (their firm).
Under What they may do, keep Auditor — they read the books and the Audit Trail and change nothing — or choose another role. Narrow it further takes away modules they do not need.
Under How long, enter the number of days their access lasts. No end date is possible, and rarely wise.
Optionally, set Period they are reviewing, from and to — for example 1 January to 31 December 2025.
Leave Require a second factor ticked, and press Give access.

With a period, their access is limited to it, and a banner on every page says so: You can see 1 Jan 2025 – 31 Dec 2025.

Journals, invoices, bills, credit and debit notes, receipts and payments list only what is dated inside the period. Anything outside it, opened by its address, is not found.
Reports — the Trial Balance, General Ledger, Profit & Loss, Balance Sheet, Cash Flow, the aged listings and the dashboard — open on the period and stop at its last day. A balance at a date inside it still includes everything before it, as any balance does. Dates wholly outside it are refused, in words.
A document or payment shows as it stood at the period's end: an invoice paid the following January is still owed.
The Audit Trail lists what happened inside the period; its chain check still covers the whole trail. The Modification Register lists the changes made inside it.
Everything else is closed to them — banking, VAT, corporate tax, fixed assets, cheques, payroll, the plugins — and so is every change: with a period, nobody can post, approve, attach or edit, whatever their role allows.

Open the person and press Remove access. Their past work stays on the record under their name.