When Skype migrates to Teams your contacts will not automatically follow. You will have to save your contacts before because the contacts will disappear during migration.
You can save a contact by right clicking and press "Copy." Write the email adress in a a document and note the name of the contact.
Open Teams and press "Add contacts" in the "Calls" menu.
Add the email you copied before and press "Search."
Now you are ready to make calls, chat and make video meetings with the contact.