To add a bookmark on the Island Browser, you can follow these steps:

1. Open Island on your computer.

2. Navigate to the webpage that you want to bookmark.

3. Click on the star icon located at the right end of the address bar. Alternatively, you can press "Ctrl + D" on your keyboard.

4. A bookmark dialog box will appear. You can edit the name and choose the folder where you want to save the bookmark.

5. Click on the "Done" button to save the bookmark.

The webpage is now bookmarked and can be easily accessed from the bookmarks bar or the bookmarks menu in Island.