A quick way to add one-time transactions or scheduled transactions in Quicken is to use the Add button on the 'In' or 'Out' portion of the Quicken Home Page.
Click on Add in the 'In' snapshot and your transaction will be classified as a deposit by default. Click on Add in the 'Out' snapshot and your transaction will default to being a payment. You can change the default transaction type if you need to.
You can now add a one-time transaction, or add a scheduled transaction.