Don't know what I have to type in setting field netmask.
Typically the netmask is "255.255.255.0".
What's the next step should I change the Lan connection to static?
You can, but you do not need to change it.
Can I use the same values from the Lan for the setting in the wlan?
No you can't, because the IP has to be unique.
NETMASK, GATEWAY and DNS are the same for all devices on your network.
Gateway is usually the IP from your router.
Router IP = 192.168.0.1
Settings on Rune
IP = 192.168.0.100
NETMASK = 255.255.255.0
GATEWAY = 192.168.0.1
DNS = 192.168.0.1
Check your router for attached devices and their IP addresses, so you get a free one.
I know this has to be static.
If your router has DHCP enabled there is no need for doing this.