To add links to your Tumblr bio, you'll need to use a simple HTML code. Tumblr doesn't give you any sort of built-in way to add links yourself, so you'll have to copy and paste the code in manually.

Click the "Show a Link to This Page" check box and then type link text, such as "Photo Gallery" or "Image Gallery," in the "My Awesome Page" field. Click the "Create Page" button.