If you're referring to a retainer, the process is different. It involves creating a liability account and an invoice or sales receipt (to hold the deposit). You'll want to follow the detailed steps in this article: Record a retainer or deposit.
We also have other articles to help you record transactions such as expenses, invoices, sales receipts, and the like. Feel free to browse them in our articles list page. Scroll down at the bottom of the page to specify your topic.
I'm keeping this thread open for any other concerns you might have for QuickBooks Online. I'm here to guide you on how to record other transactions, run reports and assist you in managing your vendors or customers.