I use a firewall with two interfaces to protect my network but I don't know witch ports to close or open in LAN and WAN interface ? thanks for your help !!
As @TeunVink mentions, you should close all ports, except only those needed for your network services. Most firewalls, by default, do not allow inbound connections from WAN to LAN. So the question is what ports should you open for outbound connections?
Here is one strategy: for a typical office, you can allow ports TCP 22, 80 and 443. If you have an internal DNS server, you can allow UDP 53 for that server only. If not, allow UDP 53 only to a few known public servers (Google, for example).
Again, this is just an example. You may have other business needs that require opening other ports.