Just building this:

I must connect two network together. "Home" and "office". Goal must be, not a few than "one network". So, instead 3000 meter long copper cable I want use vpn-tunnel.

Now ready:
"home", lan Internet hole 4G, dynamic ip.
"office, lan Internet hole 4G, dynamic ip.
Both side router is x86-based computer with i7-processor with Openwrt. Two network card, named "WAN" and "LAN". SO, both network are just standard SOHO-network.

Access server is ready and work. Installed cloud, platform named Jelastic. Ubuntu-based. So, my Access Server of the Open VPN is just as link show. Static ip, very fast internet connection etc. I can log in just as must: STATICIPMYACCESSERVER:934, STATICIPMYACCESSERVER:934/admin. Using Jelastic panel I can see my static ip and also "internal lan ip" of the Access Server.

LUCI, and also Openwrt router I can see tab "vpn".

This is not clear. Ok, I see I can make this "client luci" so I can make my Openwrt-router as client. Also this "routinv_in_openvpn" is not clear; it is my case but not just--- tunnel, but not via internet.

I am quite sure this site-to-site-vpn is now easy. But many settings are not clear... I read and read, and all manuals speak this case "but just not as just it"... Eg. Openvpn page show "how to configure dd-wrt" but it is so much different.

Any ideas?