Better explanation (for me anyway)
Bookmarklets are really powerful things but at the geeky end of the usability scale! Lets say you are using Chrome on a PC/Mac as that is easiest (not going to work on an iPad etc).
1. navigate to http://veloviewer.com/route
2. Click on Chrome’s menu (3 horizontal bars on button in top right)
3. Chose “Bookmarks” then make sure “Show bookmarks bar” is ticked.
4. You should now see a row of buttons for any bookmarks you’ve got set up just below the address bar at the top of the Chrome window.
5. Left click and drag the 2 links at the top of my route page up to this Bookmark bar. They should now appear as buttons on that bar.
6. Head on over to http://app.strava.com and click on someone’s ride so you are looking at their ride details.
7. Click the “3D Activity” button in you bookmark bar.
8. Chances are Chrome will say “Popup blocked” at the right hand side of the address bar. You need to click on that and allow popups from app.strava.com.
9. Press it again and this time a new window will open showing you all the 3D goodness!
Like I say, at the geeky end of the scale and no way to make setting them up any easier I’m afraid.
If you are using the new Routing features in Strava then if you are in “edit route” mode for a previously saved route then you can press the “3D Route” button in your bookmarks bar and see the same thing for that route.
Like I say, I will build a dedicated activitiy details page that will be just a click away from your activity list at some point but I initially built the bookmarklet as I wanted a 3D profile for a new Strava Route which isn’t available via the API and this was the only way.
Good luck!