Once you purchase the CLEAN Theme from the HubSpot marketplace, it will be instantly be added to your account and ready to use. If you're an agency working with a client, be sure you are logged in to their portal prior to making the purchase.
"Cloning" is a term that HubSpot uses for making a duplicate copy. You can the entire theme or modules within. Prior to making and major modifications to them, I highly recommend cloning the originals so that you always have an untouched copy.
I call it "fanatical support." With the purchase of the CLEAN Theme, you get free unlimited chat & email support. Along with that, I offer 2-free hours of customization support should you want me to help you make a major customization to any of the templates.
The short answer is, any way you like. For quick questions that you need an immediate answer to, try me on chat. For questions or requests that require a bit more detail, screenshots, links, etc., sending me an email is the way to go.