If you haven't already created a Tumblr blog, the very first thing you need to do is visit Tumblr.com where you will be asked to enter your email address, password and desired blog URL to get started.
Anyone with a Tumblr account can share content with other users by pressing the “Like” button or the “Reblog” button on a particular blog post. These built-in buttons allow anyone to share content within the virtual walls of the Tumblr network; however they don’t give you the flexibility of sharing content on any other major social media sites like Facebook, Twitter, Google+ or StumbleUpon.
If you want to add additional share buttons to your Tumblr blog, you need to copy and paste some code into your Tumblr blog template. Adding just one strip of code in the right section of your theme’s HTML documents will automatically place social media buttons under each previously published blog post and all future blog posts.