Logging in / Initial Setup
First, go to the Addins page (from the main screen, tap on the "..." on the bottom of the page, select Addins.
Tap on the addin you purchased. An addin-specific page should pop up.
Tap on the "Log In" button in the upper-right side of the page. (Except for OneDrive -- it's in the middle there) (If the button says Log Out, and you're having trouble uploading, tap Log Out, and then Log In again.)
Go through the Log In experience.
Once you're back to the Addin page, the button should now say "Log Out" and, for some addins (e.g. Facebook) some options should appear.
Congrats, you're now ready to upload your ride!
As to how to upload:
Uploading Existing Rides
If you'd like to upload your existing rides, go to the History page (from the Main screen). Swipe over to the History tab if you want to upload a bunch of rides, or Details tab if you want to upload a particular one.
From the History tab, tap on the left side of the screen. A column of checkboxes should appear. Check the rides you want to upload, then hit the Upload button on the bottom.
From the Details tap, swipe over to the ride you want to upload, and hit the Upload button on the bottom.
Uploading New Rides
When you've completed a ride, you're given the option of uploading the ride on the Ride Save Screen. (The screen you get to when you hit the End button.) Just check the "Export ride" checkbox before saving, and the ride will be uploaded!
As usual, don't hesitate to contact me here, on uservoice, or on the CycloMeter Facebook page.