To install the Hypothesis bookmarklet, go to web.hypothes.is/start/ and click "other browsers" under Step 2.
You will see this message:
Drag the red button with our mouse, and place it in the Bookmarks bar of your Browser.
This YouTube tutorial that walks you through the process of installing the hypothes.is bookmarklet.
If you use Chrome, see how to install our Chrome extension here.
Here's a step-by-step slideshow on adding the bookmarklet to your Firefox or Safari browser.