There are various areas where you may want to add a new client but this is most commonly done from the 'Clients' page or when you're building a new contract. Either way, when you click 'Add client' a slideout will appear.
Please remember that the client is the business you are dealing with, not a person within that business- they are termed an 'Authoriser'.
The main details you'll want to add are the name of the business and its phone number (this is the switchboard number, you can add direct lines etc. as a telephone number when creating a user).
This is any ID that you might use as a unique ID- within your CRM, for example.
This is similar to when you get all approved timesheets sent to an agency email address only this is done on a per-client basis meaning that you don't need to send the timesheets along with the invoices each week or month.
If you don't enter this at the setup stage then here's how to email your clients with all accepted timesheets after the client has been created.
Note: the "Addtional details" is a collapsible section and you may need to click on the arrow head on the right to show the fields within the details section.