Where can I change my journal series and do I have to have it?

Go to Settings - Company settings - Accounting settings if you want to change the journal series used. Here you can choose which series you want to use for a specific type of journal entry. You do not have to choose different series, if you do not make a choice, all journal entries will be series A.

The advantage of working with journal series is that it makes it easier to later trace a certain type of transaction, especially if you have a large number of entries.

Say, for example, that you choose journal series D for sales invoices. When you then create a journal entry for a sales invoice, the letter D is placed before the journal entry number in the journal entries list.

The journal series Other is used, among others, for manual journal entries and allocations.

Under Accounting - Journal entries and in e.g. the Journal entries list report, you can select a specific journal series.