Client sent a check, need to know where it goes

Hello there, jackieminsky-gma.

If the check is a payment of your client, you'll have to create a bank deposit for this one. Here's how:

1. Go to the +New button.
2. Click Bank Deposit under Other.
3. Select account and record the amount of the payment, 
4. Enter the name of your client and other necessary information.
5. Then, Save and Close.

If this is a payment from the invoice, you'll have to record using the Receive payment feature. You may want to know about personalizing the sales form in QBO. You can use this article as your guide: Customize invoices, estimates, and sales receipts in QuickBooks Online. 

Let me know if you have other questions. Take care always.