Welcome to the Community, Ras Jupiter. I'm here to help.

It depends on your business needs. I'll give you an overview of some of the forms so you know how this works in Quickbooks Online. 

For Estimates, you can choose this if you need to send quotes/proposals to your customer. This is usually used by contractors/project-based. You'll use Invoice if your business allows customers to pay later.

Here are some articles you can use for reference:

• Does QuickBooks Online support multicurrency?
• Turn on and use multicurrency.
• Create and send sales receipts in QuickBooks Online.
• Set up tax.
• Set up and send progress invoices in QuickBooks Online.
• Create and send customer statements in QuickBooks Online.

That's it! if you have any other concerns, do let me know. I'll be sure to keep an eye on it.