If you have to add a new client for any reason, you must first define all the client's data on the New client page. Clients must have an associated price list, and they may also log on to the system if you decide to give them that privilege.
This page shows basic information to get started, from creating a client company in the system to assign the client prices and logins for the users to access the system:
External companies can only see the jobs you assign to them. They do not have access to any other information, including internal comments.
Documents and translations will be associated with client companies if they have ordered services from your company and you have created a project or an order to perform them (see: What is an order? and How do external clients create orders?). Clients may also have associated invoices if you have already done paid work for them.