With a free Tumblr account, you can create unlimited blog pages, each with its own URL. Only secondary blogs can be private; your initial blog page always has public visibility. Private blogs don't contain Follow buttons because you can only follow Tumblr users, not individual blog pages.

Following a Tumblr User

From a Tumblr user's main blog page, click “Follow” to add the user to your dashboard. Alternatively, from your dashboard, click “Following” in the Account section, then enter a username or URL in the text box. A URL must link to a user's main blog page; secondary and private URLs aren't found in the user search.

Private Tumblr Pages

From the dashboard, click your username and select “Create a New Blog.” After entering a blog title and URL, click “Password Protect This Blog” and create a password. Click “Create,” then build your blog as you would your others. Invite a trusted circle of friends to the blog through email, SMS or any means by which you can send the URL and password. When invitees click the link or paste it in the address bar, they're taken to the blog's Sign In page, which prompts them to enter the password.