1.Register in https://console.aliexpress.com/
2. Create your Affiliate Application:
3. You can find your api credentials after approval:
You need to set your Tracking ID, if you want to send traffic through Aliexpress portal.
Login to your account at http://portals.aliexpress.com/
Settings → Tracking ID
You can also send traffic through any affiliate network with Aliexpress support (for example, epn.bz).