Summary:
You may want to allow specific users add and edit client information. This can be done by enabling the Clients sub-permission under Projects section in the permission assigned to the user.

Steps to enable the permission:
Log into Web TimeSheet with Administrator permission.
Click on Permissions under Users/Departments, in the side menu.
Edit the permission that is assigned to the user, by clicking on the edit button beside it.
Click on the '+' symbol beside Project sub-permission and then put tick marks in all the check-boxes beside Clients. However this will enable all the users assigned with this permission to add, edit, view, delete client information.

Note:
If you do not want all the users enabled with this permission, then you may create a new permission and assign the client sub-permission to it. You may then assign this new permission to the users who should have access to client information.