To create a new client you have to navigate into the API tab:
Click on Create New Client-Button to create a new client and name your client accordingly. Make sure you select the Scope Zeebe so the newly created client can access your zeebe-instance.
Make sure you keep the generated client credentials in a safe place - the Client Secret will not be shown again. For your convenience, you can also download the client information to your computer.
The downloaded file contains all necessary information to later on communicate with your zeebe instance:
ZEEBE_ADDRESS: Address where your cluster can be reached.
ZEEBE_CLIENT_SECRET: Credentials to request a new access token.
ZEEBE_AUTHORIZATION_SERVER_URL: A new token can be requested at this address, using the credentials.