Invoicing settings let you manage everything related to your Invoices. It has three sections, General, Payments and Emails.
In General Settings, You can set Invoice Prefix and the number you would like your invoices to start from. Like if you add prefix and starting number as INV and 0001 , you next Invoice will be numbered as INV-0001. Same applies for Estimates.
It also lets you decides if you want to apply taxes on Gross Amount or Net Amount in the Invoice. Gross Amount is the Invoice Total without applying discounts and Net Amount is the Invoice Total after applying discounts.
At the end, you can you update payment terms to be displayed on all upcoming invoices.