In order to confirm a payment has been received, click the "Receive Payment" action from the toolbar next to the desired invoice:
After clicking the "Receive Payment" option, you should be presented with a box labelled "Receive Payment for Invoice #":
You can edit the amount paid, the check number, and other information such as any notes or memos as well as the receiving account, which lets you choose from accounts you've set up in Griot. After submitting this form, you will either be left with a paid invoice or an open invoice. This depends on whether or not the payment received was equal to the amount of the invoice. If the payment was not equal, then the invoice will still be considered open.
You can view your payments for an invoice using the toolbar once you have a payment attached to an invoice, and the invoice will be considered paid once all of the invoice's amount has been received through payments.