Here's a step-by-step guide to use Open/Close Register:
Go to Settings > General > Enable daily open/close
To open a shift, head on over to Reports and click the Open Register icon
You can either enter the total amount or manually enter each amount of cash that you have.
Once you are done, click Save.
Proceed with making sales and when the shift is over, head on to Reports and click the Close Register icon.
Enter the total amount in the register, leave a note (if necessary), and close the shift