EDIT: This response is out of date, since, meanwhile, the original poster has clarified that he was asking about circuit networks and not about the item green circuits ("electronic circuits").
Here is my original (outdated) response:
In future, please post all questions regarding gameplay help in the "Gameplay Help" forum
and not the "General discussion" forum
There are many items that require green circuits ("electronic circuits") as part of the recipe to create them. I could compile a long list of all items that require them, but I don't think that would help you much. Making items just for the sake of using up ingredients is not the point of the game.
The problem you are having seems to me that you don't know what to do next, i.e. that you don't have any goal.
The first thing you should do, assuming that you have not already done so, is to complete the tutorial, i.e. the "First steps" campaign. Afterwards, I would recommend reading the official Factorio guide
. In the "Gameplay Help" forum
you will also find an FAQ
and several links to guides that may help you, including YouTube video guides. However, some of these guides may be a bit outdated, since they were made for a previous version of Factorio. Therefore, some things may look or behave slightly differently.