Configure ATA Linksys SPA 8000 and router for VOIP

Hello I need to set: my ATA device (Linksys SPA 8000) properly for my provider (Cloud Orchestra Italia). a separate IP phone (Gigaset A510IP) for the same provider. My provider has a STUN server we could use my router is netgear dgn2200 I Need to know How to set it step by step. I think there is a NAT configuration problem and I can't solve it by myself. PLEASE NOTE: I can provide screenshots quickly and work on Skype, or scren sharing, but I'm not available to give remote access to my machines Thanks