How do I configure sales tax / consumption tax if my business is not in Australia?

2 steps...

Firstly, you need to create the tax (in the admin portal). Enter the name of the tax, and the tax rate. The shortname (eg "CST") is used as a programmatic handle in various situations, so make sure it doesn't contain any weird characters. You can also choose whether the tax is applied to invoice items by default, or not, whether it is normally included in the unit price of goods, or not, and whether it needs to be tracked on purchases (usually only necessary for consumption taxes such as GST/VAT).

Secondly, you need to choose a ledger account into which the tax will be channeled. This is done on the "linked accounts" page (in the finance portal).

Once those tasks are complete, the tax should appear on invoices as you are creating them, with appropriate switches for handling non-standard items.