There's some very useful information here https://www.tumblr.com/help
Articles in this section
- Terms & Conditions - Tumblr themes
- Create a redirect
- Fix a broken Instagram feed on your Tumblr theme
- Display Instagram images in your Tumbr theme
- Display tweets in your theme
- Show notes on your home page posts
- Use your theme on multiple blogs
- Use infinite scroll on your theme
- Get automatic code updates
- Get a receipt for your purchase