Thanks for reaching out to the Community with your question! There are several different ways you can add contacts to your account. Please check out the links below for additional information.
How are you adding the contacts? Are you adding them singly? If so, once you've entered your info you'd just hit the big blue Save button on the little contact sub-window. If you're using the the type/paste multiple method, once you have several of your contact email addresses entered, if there's no issues the Continue button in the top-right corner should be highlighted and clickable.
Can you provide a screenshot (without actually sharing your contacts' email addresses) of what you're seeing so we can better troubleshoot?