If your admnistrator has enabled Time Card Approvals, you will have to submit your entire time card at the end of the pay period, when you have finished entering in your time.
You will have 2 options to do so:
If there is a time card awaiting submission, you will see a top notification to submit. Otherwise you can submit your time card at anytime by clicking on the "Submit for Approval" button.
You will then be brought to a confirmation screen where you can enter in notes to your employer before submitting:
After your time card has been submitted you will no longer be able to add to to it until the next pay period. If you submitted the time card in error your manager or administrator can reject your time card. Rejecting will allow you to continue to add time to it.