It is easy to use your Hubspot contacts in an email campaign on Skyp.
In Hubspot, generate a list. You can use the dynamic list or the static list functionality. Here is the Hubspot help article on generating lists.
Export that list as a CSV (comma separated file).
Log into Skyp.ai and create a campaign.
On the Choose Contacts page, click the ⋮ actions menu in the upper right and select Upload Contacts.
Choose your CSV and click "open" (on Mac).
The contacts will be uploaded to your Skyp account and added to your campaign.