When I add a redirect, do I type the full web address or just the part after my domain?

Either works for Old path. Wcart only needs the part after your domain, such as /product/old-name. If you paste the whole web address, the domain is removed automatically and just the path is saved.

For New path, enter a path on your store (like /product/new-name) or a full https:// address on another website.

If you add a redirect for an Old path that already has one, the existing redirect is updated instead of a duplicate being created.

You'll find this in Settings → SEO Settings → Redirects. Click Add redirect to save.