In the Firm Setup section of the firm's Settings, you'll find the Client IDs.
Manually Generated: User will create Client ID and Matter ID
Numerical: Software will generate numbers for the Client ID with corresponding Matter ID
Year + Numerical: Software will generate numbers for the Client ID with current year up front. The year portion of the ID will reset with new each year. No matter ID will be generated.
Matter-Only ID: Software will generate numerical ID for Matters only. No Client ID will be generated.