If you are not sure who your Salesforce Account Executive is, simply log into Salesforce and look for the App Called Your Account.
Once you open this App you will see your Salesforce Account Executive's contact name and their email address, or the Power of Us Desk.
Power of Us Program customers have a team of specialists called the .Org Essentials team. You can email Powerofusdesk@salesforce.com to get in touch with the team of Account Specialists who can help with account management.
For purchasing questions, you can purchase additional licenses through Your Account or by clicking this link: https://sfdc.co/ya. If you are looking to buy a product that is not on the eligible Your Account product list, contact the Power of Us Desk at the email above.