Teespring uses Airlock and Satellite Sync. You may wish to read that documentation first.

The setup process for Teespring is similar to TeePublic, so for a walkthrough of how to set up Airlock from scratch check out the Using TeePublic guide.

Products supported: All tees, all hoodies, all tanks, mugs, stickers. Probably everything else too - let us know if something doesn't work.
Title: Limited to 40 characters
Description: No limit we know of
Tags: Teespring no longer supports tags (at all)
OrbitKit chops text at word boundaries

Synchronization

OrbitKit can only update the title and description after an exhibit has been published to Teespring.

Gotchas

Before using Airlock to setup credentials, make sure that you're signed into Teespring with the "remember me" checkbox checked. After Airlock is setup, don't logout at Teespring or you'll need to redo your Airlock connection.
If your Teespring account is brand new, you'll want to enter payout information. Teespring only lets you launch a few campaigns before providing payment info. If you see BROKEN exhibits with Error: It looks like you haven't entered payout info, add this to your TS account and then select "Unbreak these" from the menu and the next retry should succeed.
Teespring has a (larger) limit on how many campaigns you can launch before making 10 sales. If you hit this limit, OrbitKit moves exhibits to BROKEN immediately. After you unlock this (a little birdie told me to buy 10 stickers), you can 'unbreak' the broken exhibits on your Exhibits page.