In some situations you'll want to put a hold on the guest's credit card without charging it, or authorize the card, and then be able to capture that charge at the end of stay. This can be done from the dashboard through the check in wizard or from the normal invoice payment screen.
To authorize a card from the dashboard/check-in wizard, select the reservation and click the 'Check-In' button. From the options listed, make sure that 'Authorize Card' is selected and not 'Add Payment'. Basically you can do one or the other, but not both. Then proceed with the check-in process, when you get to the payment screen, verify the amount and click on 'Authorize Card' in the top right.
Invoice Payment Screen
To authorize a card from the invoice payment screen, click on view invoice. Then in the transactions section, click on the 'Authorize Card' button next to the 'Make Payment' button. Verify the amount and click 'Authorize Card' in the top right.
Capturing an Authorization
To capture the authorization, click on View Invoice and then click on the authorization transaction in the transactions section. With the authorization selected, click on Capture Payment. Verify the amount and then click on Capture Authorization in the top right.