When creating any of the various post formats available on Tumblr, you can save your work as a draft so that you can finish it later. While Tumblr lets you access saved drafts directly from your dashboard, you may have to first select the blog under which the draft was originally saved to find the post you're looking for.
Get to Drafts
After signing in to Tumblr, select the blog under which you originally saved the draft using the pull-down menu on the upper right of the dashboard. After selecting your blog, click the “Drafts” link that shows up below the pull-down menu to bring up a list of all drafts saved under the blog. To start working on a draft, click the gear-shaped icon beneath a draft and then click “Edit.”