|You will need a router between the two subnets to allow them to communicate with each other. |
If you're using SOHO level equipment, you'll need a second router to give them both internet access.
If you click on my name above in my response you can look for and read my "how-to" guide on "adding a second router". The LAN port to WAN port scenario is the one you'll want to use.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.