While you are in your trial period, or if you want to try something new.... it is always bests to test it out on a dummy collection prior to making it live on your site. Set up the collection to self fulfilment (making sure you are not sending orders automatically to a print lab) and set payments to customer paying you directly (cheque payment). Now run any test transactions. Once you are happy with everything, you can delete the test transactions.
How to delete cheque payment transactions
On the control panel click "Finance" then "Sales History" then click the order id number of the sales notification you wish to delete. This will open up the order. Near the top you will see a link "If this was a test transaction, you may permanently delete this sales notification to make your reports more accurate." Click this link, and then confirm that you want it deleted. This will delete the sale completely from your sales history.
Please note you should only delete sales that are test transactions or where the sale was never completed by a customer (i.e. you did not receive the payment) to keep your sales history accurate - you can not delete sales notifications - even test transactions - if real money has changed hands.