How to get two separated connections on one cable?

The photo in your post looks about right, going by the wiring diagram here:

What you are describing is normally called an Ethernet splitter, and they are fairly cheap to buy off the shelf.

If you are connecting two PCs together directly, then you either need to ensure their NICs will crossover automatically, or use a crossover cable.

http://pinouts.ru/Net/Ethernet10BaseT_pinout.shtml so you need 1,2,3,6 to transmit and received data. Connect the socket 1,2,3,6 to the 1,2,3,6 of the cable for one PC, the socket 1,2,3,6 to the 4,5,7,8 of the cable for the other PC. At the other end, to create a cross cable, connect the 3, 6, 1, 2 to the 1, 2, 3, 6 of the socket for one PC and then 7, 8, 4, 5 of the cable to the 1, 2, 3, 6 of the socket. That's going to be some really weird connection...