Work through these in order. Each one is cheap now and awkward later.
1. Regional settings
Timezone, currency and date format, in Settings → Organization Profile. The timezone defines your day boundary and cannot be applied retroactively.
2. Organization profile
Name, logo, contact details, address. These appear on client invoices.
3. Work and time rules
In Settings → Work & Time Settings: expected hours per day, working days, whether manual time entry is allowed, how far back entries may be dated, and the activity strictness.
4. Monitoring rules
In Settings → Desktop App Settings: screenshots on or off, capture frequency, blur level, idle threshold and what happens to idle time, plus app and website tracking. Announce these to the team.
5. Roles
Look at the built-in roles before you invent your own. Admin, Project Manager, Member and Client cover most organizations. Build a custom role only when none of them fits.
6. Pay cycle
In Settings → Finance. This decides the period invoices cover and when they are cut. Set it before hours are tracked, so the first invoice covers a sensible period.
7. Projects
Create at least one project before inviting anyone. Time is always tracked against a project, so a member with no project cannot start a timer. Choose hourly or fixed price at creation, because it changes how the project is billed.
8. Rates
If you invoice: set the client bill rate and the pay-per-hour on each project, and any individual pay rates on the member. Rates carry effective dates, so entering them before work starts avoids re-pricing afterwards.
9. Invite the team
Individually by email, or with one shared link. Assign the role and the projects at the same time.
10. Get everyone onto the desktop app
Point people at Get Desktop App. Until it is installed and signed in, nobody can record hours, because there is no timer in the browser.