A credit note is essentially a document marking a return of money to your client. It could be an amount they can use in their next purchase. You may also use it to mark cancellation of a previously issued invoice.
In Elorus, you can issue a credit note to your client as well as register those issued to you by your supplier. Credit notes (both sales and supplier ones) are available in client/supplier statements. In addition, all items of your inventory included in a credit note decrease/increase your stock accordingly.
Note: A credit note is not to be mixed with an invoice with credit period regarding payment fulfilment.
You will find two related functions in Elorus. You can go to "...More > Credit notes" to issue a credit note (your client). For the cases you are the client, you can use "...More-> Supplier credit" to enter credit you received from your suppliers.
Credit will appear in related client/supplier statements (image above). Same goes for reports, such as sales detail/purchase detail.
If you wish, you can associate with an invoice/bill during the adding process. Alternatively, you can create a credit note or supplier credit (note) from the invoice overview or bill overview respectively, in a couple of clicks.