I am at a site with two separate networks - 192.168.102.. and 192,168.12..
Both have a subnet mask 0f 255.255.255.0
Both netowk switches are layer 2.
The .102 netwoek has internet.
How do I setup so that I can connect to the .12 network from the internet.

How many routers do you have on your network? If you have two, then you can add static routes to your routers for each of the networks, physically connect the networks together in the same VLAN and use your routers to route to/from the two networks. Or, if you have just one router, and since you have Layer 2 switches, you may be able to use VLAN Routing.

Here is an example using VLAN Routing on Cisco switches. You will need to enable VLAN routing to start. Configuring InterVLAN Routing  [Support] - Cisco Systems

And more: What is a VLAN?