How to forward domain to a page or other domain

> I want my other domain to open a specific category in my store

The best way to do such redirect is to use domain forwarding feature at your domain registrars (like godaddy.com). Click on the domain there, click "Forward" tab, check "Enabled" radio button and enter url you want to forward domain to. If your domain is registered with us, we can set that up for you.