How to create a new user on a newly created client

Hello guys

I have created a new client 300 using t-code SCC4.

According to the documentation the new installation will create clients 000, 001, 066 with default accounts like sap* etc.,

Since I have created a new client 300, how do i add users to this.

Right now when i try to log into this new client 300, it is asking for user name and password. Is there any default user admin name and password that gets created. If not how do I create users for this new client.

Your feedback will be greatly appreciated

Thanks