Just switched from desktop to online and need to enter last months credit card purchases so i can reconcile how do i start this process

Hello Diane145, thanks for posting on the Community page, if they have not been migrated over you can set up the account in the coa (chart of accounts) and then import the transactions via CSV file or you can manually enter the transactions into the account. 

Manually upload transactions into QuickBooks Online

Format CSV files in Excel to get bank transactions into QuickBooks Online