At fist you should know where to find the LS3. It's located in the "Custom Addon Framework" under the "Life Support Tab".
A LS3 network always needs devices that create a resource and it always needs devices that store the created resources. In LS2 you were able to link a resource creating device directly to a storage, but now you need a "Resource Node" where every device has to be linked to.

Example network:
You always need energy to power the generators, execpt energy generating devices, so you should see which method is best for you. There are three types: Solar Energy Generators, Wind Generators and Fusion Generators. For now the Fusion Generators are not really worth it so you should you Solar Energy Generators (best for ships) or Wind Generators (best for stations at windy planets).
If you get energy, the most important part is done. You can now link any energy-consuming device to the Resource Node and activate it.