Leave the ifconfig lines as in the example. Only change them if you use that subnet somewhere in either system.

You also need the "route" lines, but adjusted for your remote subnets, or at least you need one route line at one end and "redirect-gateway def1" at the other end.

I don't know what the "redirect-gateway def1" is doing. You can't have it at both ends as it say to use the other end as its default gateway which is impossible. At most only one end can use it, but it would then push all traffic from that end through the tunnel. It may be what you want, but perhaps not.

I would also suggest you use your free poweredbyclear.com DDNS in your remote lines as they will respond quicker to DDNS changes than dyndns. You also won't have to use a dyndns updater.

As both lines have dynamic IP's, you could also try adding the "float" parameter to both configs.

BTW, unless you own it, 172.45.40.0/24 is not really an allowable private LAN subnet.

Yes, i saw the HowTo of the OpenVPN, but i failed to make them communicate, if you can help me that would very nice

for example :

Site 1 :
LAN Network : 172.31.40.0/24
Dynamic Adress : site1.dyndns.org

Site 2 :

LAN Network : 172.45.40.0/24
Dynamic Adress : site2.dyndns.org


So, What are the steps to follow?

my configuration file was

For the Site 1

dev tun

port 1195

remote site2.dyndns.org

ifconfig 172.45.40.0       ## ip of Site2

redirect-gateway def1

comp-lzo

keepalive 10 60

persist-key

persist-tun

user nobody

group nobody

secret static.key

cipher AES-256-CBC

and for the Site2

dev tun

port 1195

remote site1.dyndns.org

ifconfig 172.31.40.0       ## ip of Site1

redirect-gateway def1

comp-lzo

keepalive 10 60

persist-key

persist-tun

user nobody

group nobody

secret static.key

cipher AES-256-CBC

Which end has a dynamic DNS or is it both?
The Dynamic VPN can do it for you if either or both ends have a dynamic DNS, but it is a cost option unless you run business.
It is possible to configure IPsec to do use Dynamic DNS, but really only if one end is static. It also needs the Static VPN for Business app or you have to configure it manually.
The easiest free option is probably with OpenVPN. Have you seen the Howto here? To use the console, use WinSCP for file Management and as a test editor and PuTTy as a remote console. In PuTTy, selecting text copies it to the clipboard and right-clicking pastes it into the console.