Could you maybe share some more details on what are you trying to achieve? Should the router act as a server or client? Should it use bare IPsec or should it have another tunneling protocol like GRE or IPIP as overlay for easier routing? Perhaps even consider Wireguard as a pretty good alternative to IPsec that is way easier to set up? Here is a link to a YouTube channel, where you could find some videos which could be of great help: